Yeah, but I mean from a LONG way away, with the bike whipping up and down in a blur over the whoops, and a great, beautiful din of 40 bikes all going for it. It's not impossible to tell them apart, and when it goes past you on the track you're definitely going to know, but when it's way on the other side of the track, there was occasion for having trouble. I've seen some old World Championship race videos from the early '80s, and while you could pick out the kind of bike given enough time to examine them (a second or two) they didn't always stay in view that long, especially on the natural terrain tracks where they're going in and out of trees and behind hills and things like that. It's not impossible, but having them be the same color just makes it more difficult than it would otherwise be, when the bike is at such a distance or such a angle that you can't pick out things like cylinder fin configurations, gas tank shape, Yamaha suspension, or Honda's stupid 1981 front number plate.
Of course it's gotten worse today, especially when everybody wants the color of their bike to be completely obscured by all their Monster Engergy stickers!