I know my middle sister was akin to Brady, and my parents didn't try anywhere near as much with her. It honestly sounds like the teacher is much too strict for Pre-K. That said, I think your e-mail is a great jump point. Start with "We've tried all this. [insert things you've tried.] We already know what of this works and doesn't. We're also aware that Brady has caused problems before when he's not challenged enough. What do you suggest to challenge him more? We know that coloring does nothing to challenge him, it needs to be mentally challenging." If the teacher has no ideas, go in armed with some ideas of your own. If she brings up how he's "failing the color system," that's an excellent time to point out to her what you have here: some of his infractions are ridiculous, others are part and parcel of being a kid. Yes, certain things should be immediately caught and pointed out so the kid doesn't do that again. The color system seems to harming Brady more than helping him, though. (aside: is there another teacher he can be transferred to?) Maybe go in armed with adaptations to the color system to suggest.