Here’s my first effort to do a sky a la Homer.

I tried to match the colors while they were wet and, as I should have known would happen, it dried about 2 values lighter than Homer’s original just like paint you put on the wall of your house dries lighter than it appears when wet. This made me think about the rules associated with washes. The first one is to realize that wet paint will dry lighter. Handprint discuss how light each pigment will get, but the average is about 2 values lighter.
Almost all of Homer’s washes are complex and almost break the rules. He never seems to put down a textbook wash (see below). He seems to see surfaces as complexly colored. Even what appears on first glance to be white walls are usually washed with light tints of other colors. One way Homer breaks the rule is to use “too much water” produces an interesting effect on washes that creates forms.
Here is an interesting example breaking the rules with too much water, done in watercolor, but I’ve seen the same thing when a drop of coffee dries on a countertop. Notice the hard edge:

Here’s an example of using this technique to suggest clouds against clouds which is somewhat like what Homer does:

However, too much water all the time is not a good thing. It takes a little thought to get the pigment the right consistency on your palette. Too much water and the pigment will be, well, “washed out “(meaning light in value). You want to keep the mixture rich looking. A good rule of thumb is that the paint on your palette should not run when you tilt it. It does need a little water when it comes out of the tube for a wash, but it’s best to assume that the pigment as formulated by the manufacturer is close to what you want to use. You also use water to “tint” the color, that is make it lighter in value for example to use as a skin color (You do not add white). If you give your brush a good shake after you dip it in water, that usually will reduce the water in it to the right amount to prevent it from being runny on the palette and too weak looking on the paper (assuming you are using a good watercolor brush.) It may need slightly more water to lighten it in value.
There are three approaches to putting down a wash. The classic one, almost always the first thing you read in a watercolor book, is the flat wash over dry paper, then there a wash that is laid down over a clear water base, and finally a wash that is put down over paper that has soaked in a tub for a long time (rarely done) although soaking is done to tape down paper and let it dry to pull tight.
There are three major types of washes, a flat one color wash, a one color wash that is faded out as it continues because the brush is loaded with water not pigment as one goes on, and finally there is a blended wash where the pigment changes in the middle of the wash.
There are different rules depending upon whether you are putting down a wash over new paper or whether you are putting down a wash over an existing wash:
Rules for new paper
1. Go slow. Although this sound counter-intuitive because you are worried strokes of the brush will dry before you have a chance to pick up more paint and continue, in fact if your brush is loaded enough, it’s better to carefully put in the wash because of rule 2.
To extract all the pigment a brush has to be pressed down a bit on the paper. That is you do not use the point of the brush for a wash but let the belly of the brush, halfway down from the metal ferrule to the tip, touch the paper.
From observing Homer’s palette it seems as if he does not take his color from wells in the palette and put it in the mixing area. What he seems to be doing is to put dabs of pigment on the mixing area apart from one another and then mix them in the middle. It’s rather hard to get enough pigment into the mixing area from a dry cake of pigment, so if you’re doing a large wash like a sky, it’s probably better to follow what I believe was Homer’s approach.
2. THE MOST IMPORTANT RULE: Absolutely no corrections. Any correction will leave a mark of its own and disturb the flatness of the wash or even pick up pigment and leave the area whiter than the rest. I find this very hard to follow, but all corrections must be done over an absolute dry wash.
3. Light to dark washes. Start with the lightest color you see even if it is hardly important. For example, an intensely color object (a flower) always draws your attention to the brightest part and you are tempted to put that color down first. It would work better to find the lightest (closest to white) part of the flower and do that first. Often it is not white but slightly off white. For example in the Homer sky above the white looks to me like it might be slightly pink. I haven’t seen the original but before pollution the sky was often somewhat pink at the horizon (now it’s brown.)
4. Let washes dry completely. This produces a hard edge. Do not let wet or even damp washes touch. Beware: washes will spread out a little bit; and, if they are too close to another wash, they will “blossom.” See below. (The bottom yellow form did not touch the blue when I put it down but notice there is a little yellowing anyway.

5. You can tilt the paper any which way to make the water flow in the direction you want.
Washes over other washes
In his skies Homer often has a particular effect in which the a cloud form is light in the center but around the edges it is dark and the edge is hard. This accomplished by first putting down clear water in the shape you want and introducing pigment into it. This can be done on dry paper or over a dried wash of color. When you do so, the pigment migrates to the edges of the wet area. I have experimented with wetting four areas all the same size and putting into the wash some color at 5 , 10, 15, and 20 minutes after putting the water down. I noticed very little difference. The final water blob I let stand for 20 minutes and then used a paper towel and bloated up most of the water that was standing on the paper. Even so the result didn’t look much different. There was a slight trend for more pigment to stay in the center of the wet area, but it was hard to measure the amount of pigment each area received. My conclusion is that not much is achieved by waiting or my blotting.