You could apply effectors to change, say, the object color (making sure to put the effector in the Letters tab and not Lines or Words) and then base your shader off of the luminance of the object color.
You could also do this in Cinema 4D, yes – no question.
I think you can even do this with Cinema 4D Lite that comes for free with AE, but I’m so used to the full version, I don’t quite remember what is included with Lite.
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