The trouble from a vendor’s perspective is that the perception of color is extremely subjective. Perhaps you remember the colors from the first DVD release of the show, where there was little-to-no color correction and the science color looked downright green. Or maybe you watched the show on an aging family TV set, where it appeared a deep blue…?
That presents an impossible situation. Given the potential factors of stage lighting, film stock, post-production color-correction, etc, etc., the only available option for an ‘objective’ color reading is that of the actual fabric in the costume.
Of course, even this isn’t simple, as there are inevitably slight variations from one dye batch to the next as well as differences in how the dye looks on different fabrics (i.e. spandex vs.wool gabardine). My favorite example of this is a shot in the seventh season episode “Phantasms”, where Data and Worf are flanked by 2 security personnel (all in frame, all wearing gold (2 wool, 2 spandex)) and out of the 4 gold costumes, no 2 of them quite match.