The wine was heavily spiked with drugs to knock Alex out, which could have diluted the color. In the scene Alex is clearly suspicious of the wine, the appearance of it, the odor, and keeps stalling drinking it. The off color says "something is wrong with this". There are other cues in the scene that are designed to give an unsettling feeling, like how in different shots the wine levels in the glasses keep changing.

Kubrick was also known to put continuity errors into his films (The Shining is full of them) to create an uneasy feeling in the audience. These aren't mistakes, Kubrick was meticulous in his technique, he was famous for making actors take dozens of takes just for one line of dialog. Could this just have been sloppy work from Kubrick? Maybe. But knowing how much a perfectionist he was makes me doubt it.