I really don't know how I imagine him nowadays. It depends a lot. It is a mixture of PJ's monster-like dark Gríma and a blonde acne-faced version I have for some reason. And it is very difficult to totally banish my childhood image of him, which was something like this:
Yes, I pictured him with green skin with pink and yellow spots or warts.

I think I maybe imagined him to look a bit less reptilian than in that pic but I never was good at drawing profiles, especially not when I was a child.

And he is also intentionally depicted as short and crouchy.