I have read and listened to information about color. There are a few things that seem to always be said, but I disagree with some of them. I have listed a couple of them with the reasoning behind my thoughts. You may disagree with me.
Mix more than 3 colors and you will get mud. I've heard this several times. I disagree wholeheartedly with this. As with many artists I know, I save my left over paint and have my "mud" (grays) for the next day. I don't know how many colors of paint that pile has in it, but it could be 7 or 8 plus white.
Each day I start with that left over pile of gray. When I need a gray, I will start with that pile and modify or change it to suite my needs. The grays or "mud" that I use are very important to my paintings and I use them in every painting that I paint. The reasons your painting may look "muddy" may be because you have used and inappropriate color in a space, the wrong temperature or that you have worked two different values together instead of laying down nice clean strokes.
"Mud" can look "fresh and clean" with strong, confident brushstrokes. Another common fault is to add too much white to a color. Titanium white, which is opaque can make a color chalky or in some cases "muddy".
So, the solution would be to learn about your colors and how to mix anything you want. Also, don't overwork your paintings. Learn to lay a color down and leave it alone. If it isn't right, scrape it off and try it again. The featured painting is one in which I used my left over grays from the day before.
I'm sure you've heard the advise, "never use black in your painting". False! Now, I don't often use black, I admit, but that doesn't mean that there isn't a place for it. In some paintings it may be perfectly appropriate.
Some ways that I have used black is to add it to some of the dark colors on my palette. It especially works well mixing it with alizarin crimson or viridian. If I want the black to be used for a dark color, I will modify it with another color, just as I would for my other darks. I also have used black to gray colors, adding a very small amount. It doesn't take much.
Black also makes a great warm green by mixing a yellow to it. Now, a word of caution: I wouldn't recommend black for the beginning artist. Black can be difficult to learn to use. When artists do use black, it is often overdone, a little bit goes a long way. I won't say never use black by itself, but certainly don't use it often or in excess in any one painting.
Remember the rule, save your darkest dark (accent) and lightest light (highlight) for no more than ten percent of your painting View my video, mixing paint with a limited palette. Both of these will give you a better understanding of how to mix the correct "mud".