Absolutely not. Some guys like pale legs. It would be stupid for someone to think someone isn't attractive because their skin isn't tanned anyway. The fact that your legs are pale doesn't change the shape of them, so it can't make them less attractive. :)
i don't even check out the person beside you and I'll tell you why. the people who are truly out there to work out, are working out, they could care less what your legs look like. shouldn't worry too much about that.