Good point, Sauske can't actually tell what type of chakra is used by color either. Thank you krazykwasi for pointing that out. Also note that the sharingan is the only genjutsu known (to us) that needs eye/eye contact. Plenty others have been used (think of any other illusion in the series thus far) and you will see they can affect groups.

And if you guys really want to continue the arguement of Sharingan beeting the illusions of men in the chonin exams, they didn't have any chakra circulating through them, so for Sauske it was easy to tell since he could see them. If he couldn't see them, then diffrent story.