Today, my daughter will mostly be wearing...

[Ryft]

Theists have theistic things to be fundy about that atheists can't.

The accurate flipside of that? "Atheists have atheistic things to be fundy about that theists can't"—

—since no theist will agree to something atheistic, just as no atheist will agree to something theistic. Hence my point that "fundy atheists" are fundy about their atheistic views (as opposed to just any view an atheist can hold, such as "American muscle cars are the best"). Theistic views are views which are predicated on Deity Required (e.g., intelligent design). Atheistic views are views which are predicated on No Deity Required (e.g., natural selection). It is a stark antithesis.

Theistic belief systems have colour

Atheistic belief systems don't?

[Theistic belief systems] have beliefs to them

Tautology Alert! (Oh, and atheistic belief systems have beliefs to them, too. Also tautological.)

Atheistic [belief systems], however, are basically any belief system whatsoever that is without a God.

No, atheistic belief systems are those which are predicated on No Deity Required, which theists cannot agree with. For example, if your view of morality posits No Deity Required for morality to exist and be meaningful, then it is atheistic.