Since the colours were added to item names, searching in the market filters to items with a match for your search in their colour names.
For example:
I noticed this while starting to search for ranarrs. If you type 'ran' you will see all rares because they use @ran@
Searching for 'red' to find red h'ween or dragon masks etc also finds comp bows, ultimate slayer masks and anything else using @red@
Searching for 'bl' shows everything using @blu@ and @bla@
..and so on