Orange was a color.
In 2370, upon learning that Paul Menegay's clay sculpture had won the Captain Picard Day art contest, William T. Riker inquired whether it was "the orange one with the lumpy skin", which Jean-Luc Picard confirmed. (TNG: "The Pegasus")
In 2371, Julian Bashir cautioned Kira Nerys not to replace the carpets in Deep Space 9's guest quarters for the visiting Yalosian ambassador with anything red or orange, as they didn't see that part of the color spectrum. (DS9: "Improbable Cause")
In 2372, The Doctor became aware of Tom Paris' romantic interest in Kes upon noticing the orange coloration of the tips of Paris' ears when she entered a room. He had initially attributed the symptom to Tanzian flu before making the connection. (VOY: "Parturition")