If you haven’t painted on a particular work for a while, as I often do, in order to keep your painting uniform in color in oils or acrylics, squeeze out the same colors you already have on your pallet, even if dried up. I don't restart with different colors. I usually only use about seven colors because it's easier to blend colors for the overall painting. Introducing a new color can conflict with the general harmony of the work and is not always easy to fix. The colors you have on your pallet are the color of the overall painting. They should be in harmony throughout the painting, the exception being a subject that must stand out by itself, such as a light or or lamp.
Too many colors can get confusing.
Using yellow, red, blue and white can result in a complete painting if you know how to mix them in the right proportions. I usually use these colors plus dark green and purple. I name the colors this simple way here because the color names are different, depending whether using oils or acrylics. Green for example can be named hookers green or sap green. They are still green.
