What does a white spot on your iris mean?

Unusual if not Blue: Actual "spots" on the iris are unusual. Some area may be white in blue eyes, but not really sure what you are asking. Has it been there a long time? Is it growing? Are you sure it's the iris?

Normal variation: Irises have a variable surface pattern which sometimes includes one or more whitish patches integrated into the pattern. These are benign and add to the variety of our appearance. Rarely it could represent a tumor but these are generally dark and of course may increase in size. Be sure you are seeing your iris and not the cornea which is the window in front of the eye.