Inspired by Lewis Carroll's book "Through the Looking Glass," Yasmin Sethi created this Alice chess set where the pieces are opaque until they are put on the board - then they magically turn transparent to reveal their identities.
Link - via DVICE, thanks Sheldon Price!
Second thought: how inconvenient for initially arranging the pieces on the board.
Thought after reading the comments: I interpreted that "off the board" value as in when a game is not in session and the pieces are just stored away. Outside the game entirely, each piece has no more significance than any other. Also reminiscent of the prover, "when the game is done, the king and the pawn go into the same box."
Reminds me of the glass with a picture of a bikini-clad woman. When you put liquid in it, the bikini disappears.
Now there's a concept.