I can honestly say that I've never used the word orangest, and I can't recall having ever heard or read it. I've heard greenest, bluest, and reddest. I don't think I've heard yellowest or purplest, although they both are recognized as words. This is pretty strange. Perhaps if enough people add it to their words, we can start a movement for the dictionaries to add it. Anyone know a lexicographer?
But some dictionaries do not leave the comparative and superlative forms as implicit, yet no dictionary (even online) lists oranger and orangest. Try reddest or purplest in OneLook. Then try "orangest". Is there any other ordinary word that has been part of the language for hundreds of years that is not listed in any dictionary?
Why is "orangest" not listed in any dictionary? Its meaning should be obvious to any English-speaking six year old. It gets 23,000 g-hits and dozens of genuine uses turn up in searches of Google books and in Amazon books. Comparatives and superlatives of other common colors are listed in at least some dictionaries. Why is orangest ignored?