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, blackness, inkiness-the quality or state of the achromatic color of least lightness (bearing the least resemblance to white). whiteness, white-the quality or state of the achromatic color of greatest lightness (bearing the least resemblance to black).