Even if colour blindness is commonly called by this name, color blindness is not a form of blindness at all, but a deficiency in the way a person see colours.
Colour blindness (or, more accurately, colour vision deficiency) is usually an inherited condition that affects males more frequently than females. An estimated 8 percent of males and less than 1 percent of females have color vision problems.
Red-green colour deficiency is the most common form of colour vision deficiency. Much more rarely, a person may inherit a trait that reduces the ability to see blue and yellow hues. This blue-yellow color deficiency usually affects men and women equally.
Look at the image below and check if you see a strong change in colour brightness or if only the brightness varies.