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.
Black is the darkest color, resulting from the absence or complete absorption of light. Like white and grey, it is an achromatic color, literally a color without hue. It is one of the four primary colors in the CMYK color model, along with cyan, yellow, and magenta, used in color printing to produce all the other colors. Black is often used to represent darkness; it is the symbolic opposite of white (or brightness).