Working with a single color theme naturally puts the painting in a tonalist category, I'd say almost by definition because you have to do most of your composing with shifting values.
It's simpler than using a lot of colors, but the flip side of that is you cannot hide behind splashy colors. You really have to have very good value control to pull this off.
The idea is not complicated. You basically pick one hue, and paint more or less monochromatically, and strategically adding a little bit of color shifts to make the painting seem less monochromatic.
That's about as close to a formula as I can get! (there's that F word~) But let me talk about each painting and see if I can pull out some of the things I did which deviated from the strictly monochrome structure, because that's where we can add a little bit of complexity and interest into an otherwise very limited color space.
The top image of the delta, obviously, has a violet themed structure. It never gets very saturated, which help to maintain a quiet, somber mood. If you look closely, the very distant mountains(?) and the sky are slightly different in temperature - the sky has a tiny bit of red in it, which differentiates itself from the cooler hills. This is subtle, but not a tricky color shift because violet is made from blue and red. Adding a little bit of red warms up the color, and adding blue cools it, and we don't have to worry about the new mixture being out of harmony.
The darkest land mass in the front has some Transparent Oxide Red in it. Which, if you think about it, is still red. The TOR is used, then, to control the saturation of the violet so that we don't have a screaming purple. Another way to control saturation is an addition of a low chroma blue, instead of (or together with) Ultramarine or another intense blue. For this I probably used Ivory Black as a low chroma blue.
One more thing about controlling saturation. (Because you know, I'm a little shy about using loud colors) Ultramarine is already a violet-leaning blue. Alizarin is a violet-leaning red. They are both very intense colors, so if you mix them, you get a very intense violet. Great, if that's what you're looking for. But if you want a little less intensity, you can try Ultramarine plus an orange-leaning red. The orange being complementary to blue, the resulting violet is much more muted than if you mixed Ultramarine and Alizarin. Because nothing I paint requires screaming violets, I like to use the mixture that's already a little muted even before I gray it down further with Black or TOR.
Green. The color shifts toward yellow a bit as the values get lighter. It doesn't have to, but that's what I chose to do to deviate from a strictly green painting. I also used TOR in the underpainting and the darks of the foliage interior. Red is complementary to green, so it helps to gray down the green if you mix them. If you juxtapose them without mushing green and red, you start to get simultaneous contrast, a little bit of which helps to break up the monotony.
Mixing Ultramarine and yellow ochre, the resulting green can't get too saturated even if you want it to, so that's a good way of limiting your intensity. You can always add Cads later if you need to punch up an area.
I tried to get some color variation in the ground plane, mixing the same three colors plus white (Ultramarine, TOR, and Yellow Ochre) in different amounts to get different, yet very closely related notes.
Peachy! Or red orange. The single color theme sometimes isn't strictly single colored. Sometimes it's better described as a "narrow slice of pie". The pie refers to the familiar color wheel, and narrower the slice, the more specific the hue. If you cut a fat slice of pie, you're basically using analogous colors - neighboring hues such as red and orange, orange and yellow, etc.
As long as the slice of pie isn't too big, it still works the same way. In this painting, if you ignore the violet in the distant tree masses, we basically have an orange themed painting, but the lither colors (sky) has more yellow in it, and the darker colors leans more to the red slice of the pie. We are not seeing bright yellows, oranges and reds because saturation is kept in check. In this case, I'm reserving the saturated (relatively speaking) colors for the lighter range of the value scale. In the shadows, I drop not only the value but the saturation as well. Can you use a saturated dark red in there? Sure you can. But you have to ask yourself, what's making it so bright in the shadows? The color of the sky affecting the dark areas, where it's not even facing the sky? Might make sense if someone was having a bonfire at the base of the trees. The point is, without a good reason, pushing color becomes a purely subjective decision, and the more you do it, the more you deviate from a structure that makes logical sense. What's wrong with that? Nothing, but if the painting ends up not describing a convincing light / atmosphere environment, that will be the price for your expression.
The little bit of violet in the back trees is a deviation from the slice of the pie. But not by much. The violet leans heavily toward the reds I used, and the yellow's in there too, to tamper the intensity and ensure harmony. The saturation and value are kept in check so that the violet, even though it's different from the rest of the painting, doesn't stick out.
Yellow. The lighter end of the scale is obviously yellow, and the darker end - I needed to go very dark - becomes a very grayed down dark warm color. Grayed down because at that value, we can't tell a yellow from a red. But kept warm (it's a reddish brown, very close to black) so that it harmonizes with the yellows. To ensure this, I used TOR and black both in the very dark areas, and in the very light areas. The yellow sky isn't very intense after all; the impact comes not from the yellow color, but the strong value contrasts.
This painting is a little more complex than the previous ones in that color deviation from the single-color structure includes introduction of local colors. The green of the trees, for example. But notice that only the trees in close to the viewer is green, and the far ones just become darker version of the yellow /brown structure.
And, the greens you do see are not super green. They're more like green versions of the foundation color. I figure out the value that these greens need to be, and nudge the yellow/brown in the direction of green by slowly adding green into it. It helps to use the same yellow (ochre, in this case) to make that green. This way, I can maintain close harmony and the look of a very tonal painting.
The same thing is done with the violet grays of the pavement. They're just slightly violet version of the yellow/brown that I started with, and nudged the colors a little bit at a time till I got what I wanted.
The big exception is the bright red I used for the tail lights. Why does it work? Because 1)they're accents, used very sparingly. and 2) they are their own light sources. Because a tail light is a light source in itself, it can have its own color, especially if they're close to the viewer and are being less affected by the colored atmosphere that we have established.
Peachy again, with some local colors used as accents - the green of the palms, the reds of the tracks, and a few small spot colors on the figures at the bottom. But again, these colors are used very sparingly, and are nudges versions of the foundation colors. The red can be pushed without going out of harmony because it's part of the peachy DNA.
Blue! The dark areas become almost black, but still has a lot of blue in them. In the distance, I have a few different color shifts - some violet, which is a closely analogous color to the main blue, and green in the trees, which is also a closely analogous color, but on the other side of the slice of the blue pie. They're both nudged versions of the blue.
The sunlight in the distance is a pale yellow, but it's not very saturated at all. It does have blue in the mix, along with a bit of black, but the biggest common denominator between that pale yellow and the blue is white. You can see that the blues, especially surrounding the pale yellow sun light isn't very saturated, and the values are closer to the yellow.
To further integrate the yellow into the otherwise blue painting, I brought it in to the big field of passive area near the bottom of the painting. The Double yellow line helps to tie them together, also, but that's getting into the accent for expression's sake domain that I mentioned earlier.
And the red tail lights again. I can get away with using bright reds because they're light sources, and used as bling.
This last one is built on a muted red-violet structure. The color deviations are either analogous (pavement), nudged local color (yellow bus) or light sources (tail lights). All other variations happen within the slice of the pie.
It's a simple system, but when you put it together with slight variations, you can end up with a painting that doesn't feel monochromatic, yet very tightly harmonized. I love working this way because it's logical, yet allows for a lot of subjective variations, and I can push and pull between simple monochromatic structure and complex combinations. Tonal paintings are very effective in creating the kind of mood I want to express, and building on a single color structure keeps things from getting out of control.
Boy that was long winded! Thanks for reading till the end! Happy Holidays!!!