A more suitable indexed image archive
Chromatik doesn't appear to be a reliable image index, because of the lack of support by its operatorExalead. Possible alternatives are:
Flickr
well supported and reliable
only 16 colours available and multiple colours per query (undocumented, but available)
search by (visual) types and categories (undocumented, but available)
Imagga multi-colour search
not yet available, but free access, as soon as testing begins
intelligent colour clustering
full RGB range, up to 5 weighted colours per query
can distinguish between foreground and background colours
Picturelicious
requires self-hosting
only clandestine image archive use readily available
very simple indexing approach, no clustering
full RGB range and an arbitrary amount of colours per query