You can, and often will want to, paint on top of other paint. You usually wait until the underlayer is dry before adding another layer of paint.

What you put on top influences what is underneath, and layering is one way to mix colors. Keep the paint transparent so you can see through it and into the layers. This makes deep, interesting paintings.

Create several rainbows of color with this layering exercise.

Get a quarter sheet of watercolor paper. This can be a square piece of paper.
Activate all your paints. You want to become familiar with the entire palette of colors, so use them all.
Paint a stripe of each color on your palette from the top of the paper to the bottom, leaving a small stripe of white between each color so they don’t mingle.A 1/2-inch flat brush is just the right width for each stripe. Keep the colors strong by not diluting them with too much water. You could make another chart with pale colors and see what happens with those, too.
Let the stripes dry completely. Use a blow-dryer, or be patient and make a cup of tea.
Paint a stripe of each color horizontally, moving left to right across the paper (or right to left, your preference). This puts each color underneath and over the top of all the others.
Let the paint dry and analyze the results.
Label the paint names for a handy reference chart.

This simple chart gives you a wealth of knowledge about colors and color combinations. Each intersection displays a new color. Look at the differences when a color is on top of rather than underneath another color. Some colors are transparent (see-through); others are opaque (solid), no matter how much water you dilute them with.

For bonus points, try lifting a small area out of each stripe of color (the previous section tells you how). This shows you which colors are easy to remove and which are staining. The staining colors never lift back to white.

This author writes about woodworking Jointer Push Block and Stream Online Movies. Visit the Snowman Yard Decorations website for unique Christmas decoration ideas.