It is possible to add another color channel, but to be able to drive it with video we'd need to find a rgb value that can be used to represent that channel's output when hitting a white surface.
Since this fixture also incorporates a white channel we're only able to use two color components at most for any other channel (since the lowest component is zero'd out and sent through the white channel instead). For amber we're using
255, 130, 0. This works because it only uses red and green. For purple we'd have to use just red and blue. Would you say that something like
179, 0, 255 would be an accurate representation of the uv channel's output?