I'm meta-religious: I follow whatever religion it is necessary to name for my answer to this question to be this answer.

Eh, circular logic theology is so 11th Century Catholicism.

Edacade's right that under current rules a colorless color indicator just doesn't actually work. Buuut that doesn't really mean much, because if R&D did decide that a colorless indicator was a good way to go about things, they could just change that rule so that it does work; the rules are only ever set in stone insofar as WotC wants or needs them to be. If R&D needs them to change, they'll change.

The better reason not to use colorless indicators is because it might not work all that well. Players are very used to looking at cards' mana costs to determine their color--sure, they normally look at frames, but when confronted with an unhelpful frame (like, say, the ones three- and five-color cards have), they look at the mana cost. If R&D was only using the color indicator and frame, there's a significant risk that some players would see a weird frame and not know what it meant; they might end up mistakenly thinking the weird frame merely indicated "Eldrazi-ness" and the cards were colored as normal.

Look at Garruk, the Veil-Cursed. He uses a hybrid frame rather than the normal multicolor one because R&D wasn't sure that the latter would convey the color well enough in the absence of a mana cost.

They should use the hybrid frame for every two-colour card anyway. IMO.

I like reserving it for the hybrids, myself--giving each a unique visual treatment makes it easy to tell them apart at a glance.

Anybody think a completely 2brid monocolor card should get a colored/colorless hybrid frame? I think that would look awesome.

This Forum is called Rules Central; please discuss aesthetical preferences elsewhere.