Here is a terrific site where a guy takes the description of characters from works of literature and then creates their face using police ID software (modern-day indentikit or photofit). No Bradbury characters on there, but there are some others you will surely know:

http://thecomposites.tumblr.com/

Wow, way cool idea!

Bradbury's novels being short on description anyway, and especially the ones put together of short stories with things not necessarily in order, I was left to picture the characters for myself. A general rule in novels is if characters are described, descriptions should occur near the beginning! It isn't until practically the end of Dandelion Wine that he says Douglas's hair was fair or light, by which time I'd already long since pictured a dark-haired Douglas and read it that way every time. The only other description that I know of Douglas is that his skin was very dark--he was a tanner, not a burner--no other physical description I can name.