Quoted from Jigs:My Stellar Wars plastics looked just as black as yours when I sold them at a swap meet back in 2014. I actually have the pf in my game room currently because I've been pulling wires to match a game being worked on. Don't call me a dick, but these are dirty old plastics. Mine looked identical.
I am not calling anyone a "dick" but I am 66 years old and have been dealing in antiques & collectibles for over 50 years and I have never seen dirty blue turn black. I am sure this isn't the only set out there like these and I am sure some of the other colors are off on these because of the yellowing but yellowed medium blue is not going to turn black & if it was due to UV rays or "sun fade" blue would typically turn lighter not darker.
In any event it isn't any huge deal I just thought it was kind of interesting and after spending a good bit of time on the internet looking I didn't find another machine or plastic that looked like these. Maybe the set you had was also from a prototype or something? I am just hoping to hear from someone else who might know more about these but since I don't own a Stellar Wars machine in the end it really doesn't matter to me.