I've owned white Burton Moto's, didn't have any problem with them getting clean. Dirt happens and it will show up more on white but they are boots, you can just wipe them off. Dirt you pick up on the walk from the parking lot typically is gone due to a day spent riding in the snow. Dirt on the way back to the car can easily be cleaned up if you're really a big clean-freak but it was never a problem to any degree for me that I even needed to do it.
I'd be more concerned about Moto's in any color, I found them to be a pretty poor boot.