(Actually aren't "psionic" and "psion" terms made up by D&D?)
No and maybe. "Psionic" first appeared in science-fiction, in the 50s, a portmanteau of "Psi" (the letter that begins Greek words like Psyche) and "-onics" the 50's version of ".com" - it was meant to suggest psychic powers that could be improved by study and/or technological augmented.
(I guess I better expand on that. Back in the 50s there was some pretty impressive growth in electronics, and '-onics' started being appended to all sorts of stuff to create company names or exciting new trends or whatnot that sounded all modern. Kinda like how investors would throw money at you if you put .com at the end of your business name in the late 90s. "Pets.com? We can't loose!")
"Psion" meaning "person who uses psionics" might've been D&D's fault, (2e also used Psionicist, BTW.)
They are legitimately two different words with not quite synonymous meanings in English. The actual definition of Sorcerer is closer to a D&D warlock, though.
lawful vs. good, chaotic vs. evil (earlier editions definitely treated lawful as the alignment for heroes and chaotic as the alignment for monsters)
Probably borrowed from Michael Moorcock - the struggle between Law & Chaos (with neutrality also in there) was a overaching backdrop for many of his books, an alternative to the classic Good v Evil. Moorcock enjoyed tweaking things, that way.
dragons are color-coded for your convenience
Color coding mapping to breath weapons might be D&D. But dragons of specific colors have been significant in heraldry and in myth/legend. The Red Dragon of Wales, for instance.