I'm not at all confident in this card. Atomistic Metaphysic is pretty sketchy on its own, but adding the tap to make colourless ability makes this card seem very confused. But I need to give creatures tap and target abilities so that Atomistic Metaphysic is relevant. Instead of attaching a useful tap ability to this card, I went with something that seems reductionist, that is, rendering other creatures colourless. This will be relevant against some Black cards in the set, but it's pretty wimpy all the same.

This is effectively "Tap enchanted creature: Untap target permanent", which is usable in some circumstances.

I suppose my worry is that, if someone like me opened a pack and saw this card, he or she would immediately ignore it just because the tap ability seems so meaningless. On top of that, this ability is only meaningful against Black, which is supposed to be Blue's ally. And on top of that, colourlessness is a better fit with White's flavour in this set (since White represents the Universalist philosophy that holds that everybody is governed by a single overarching moral order, all Colour philosophies are meaningless, etc.).

The atomistic bit might be clearer as just: ­: Target a creature.

But if the colourless bit is important... yeah, you're a bit stuck. Dunno what to suggest.