Look at the number Mod 1. When you look at a number Mod n, you just divide by n, and look at the remainder. So here you divide by 1, and the remainder is just the fractional part. The best way to do this depends on the language.
Simple paint a long horizontal black stroke on a scratch piece of paper and then once it dries paint your watercolors colors in short vertical strokes on top of it. If the paint appears to sit on top of the black stroke the paint is opaque.
In the print industry, cyan, magenta, yellow and black are used as the primary colors. When you mix all the colors, the result is gray. If you look at a printed page with a magnifying glass you might see something like the illustration below. Explore another dimension of color at the Color Matters website.