Thanks for all the great input - I'm going to go for it!
On Jul 31, 2010, at 12:27 PM,
How about X + Red=Orange
Y + X=Green
solve for Y
then there's always the word problems
Sally is dressed from head to toe in X, but doesn't want to clash with Jane who is wearing green which is X's complement. "Together we will look like a Christmas tree" she wailed.