This riddle is a "thanks" to user477313 for his Grandpa Puzzle.
" I just got back from visiting my cousin Bob" said Grandpa
" There at a beer party I met two of his friends who claimed they were completely color blind. So I showed them three cups. One was brownish, one was grey, and one was bluish grey looking. Pretty close actually.
I asked them do they see or recognize any color?
And they both picked the Grey! Not the brownish, not the bluish but exactly the Grey.
Dang. Can you explain this son?"