"BLUE BALLS" is the popular slang term for vasocongestion in the male genital area, characterized by a dull pain in the lower body.
The testicles do not actually turn blue. Instead, a bluish tint appears on the skin of the scrotum, although this may not happen in every case. If the male reaches orgasm and ejaculates, the arteries and veins return to their normal size, the volume of blood in the genitals is reduced and the penis and testicles return to their usual size rather quickly.
If ejaculation does not occur there may be a lingering sensation of heaviness, aching, or discomfort in the testicles due to the continued vasocongestion. This unpleasant feeling has popularly been called blue balls, perhaps because of the bluish tint that appears when blood engorges the vessels in the testicles.
