Here is a picture which, I believe, shows well the results of BYU's efforts to get fans to wear blue to the game:
The effect is noticeable, especially when contrasted with Arizona's fans to the left, but dark blue is still a tough color to get to stand out. Even more than the white shirts, the arms of fans break up the sea of blue-- and there's not a lot that can be done about that, especially during the beginning of the season. The white shirts stand out quite a bit as well.
I was still relatively pleased with the result, though, and I think the next few games should get even better results. The fans that realize they were supposed to wear blue to the game on Saturday should still wear blue, and there should be some that got the message.