Here's what I think:
Sometimes, you can't find the spam people made. You clear it with /clearspambricks.
However, it won't affect you if you're not able to see it, because it's out of your view cutoff and won't be proccesed, so basically, it doesn't matter unless people are standing near it and are complaining to you. In this case, just destroy the baseplate. If there's no baseplate, you just clear all of that person's bricks.
Clearspambricks shouldn't clear red bricks. It's pretty stupid, because not only is red a primary, and important, color, but 1x1's can be used in various, useful ways, especially when red. In the case of being worried about someone coming into your server and placing a bunch of red 1x1's all over, you could just either ban them, or put a password on your server if you're such a paranoid weirdo.