Oracle cells usually devour everything, unless they're controlled. So they can change almost anything.

[Little bit of fridge horror for the general populace there.

Honestly, if he were to explain everything Oracle cells could do, he probably would have scared way too many people, so he's chosen to dole it out in small and digestible installments. Also he doesn't actually know all the details, RIP.

Now he's caught up in trying to picture Marisa with red hair, though, so he's the one staring a little.]

... Hmm. So you can change your hair to any color?