From Annenberg Learner:
Because the X is inactivated randomly in cells, one cell could have the maternal X inactivated, while the adjacent cell could have the paternal X inactivated. This causes a pattern of gene expression called mosaicism, which occurs when different alleles of X-linked genes are expressed in different cells.
However, this seems at odds with colorblindness being more likely in males. From Wikipedia:
The genes that produce photopigments are carried on the X chromosome; if some of these genes are missing or damaged, color blindness will be expressed in males with a higher probability than in females because males only have one X chromosome, whereas females have two and a functional gene on only one of the X chromosomes is sufficient to yield the necessary photopigments.
Question: If X chromosomes are randomly inactivated cell by cell, shouldn't the fully functional photopigment-producing gene be inactivated approximately half the time? In which case, wouldn't we instead see females with colorblindness with higher frequency as males, but experiencing colorblindness to a lesser extent? (After all, two X chromosomes means two chances for a dysfunctional gene.)
I'm guessing I'm missing a piece of the puzzle here, e.g., perhaps the relevant cells "know" to inactivate the dysfunctional X chromosome, or perhaps it's to do with X chromosomes only being incompletely inactivated.