I'm not the op, but I have the same grapheme–colour synaesthesia, and I perceive Google's logo in its original colors. But if I look at the word Google in plain text (or imagine it in my mind's eye) the coloration is different. [G] is kind of a brown, the [o]s are black, the [l] is white, and only the [e] at the end has any color, a bright green. I have to think about the individual letter associations; the brown and black dominate my perception of the word itself, but the vowels are a bit brighter. It's... kind of hard to describe, I'll admit.

I guess I should stress that I don't "see" these colors. I just know, intuitively, that they are there. They are the color of the letters in my mind's eye, if you will. I suspect thus that it has nothing to do with the shape of the letters, but is a side effect of how my brain processes the language, and understands the underlying phonemes. That would also explain why the vowels seem to be so much brighter, since they are the most important letters when I'm scanning text quickly for comprehension.