I'm still not convinced. They said the answer is pink. But...it wasn't pink, even to their own admission. A pink shoe, when placed under pure-green lighting is no longer pink: at this point we're out of illusion territory and into lighting trick / semantics territory.
If they'd have said the answer is green-gray, then fine, this would be an illusion for those people who incorrectly thought the shoes are pink, but their answer is still wrong.