I will take a stab at this. According to Orchid Wiz, there isn't a Brassia called Dark Star. Since Brassias are heavy on the chartreuse shades, I guess this makes sense. There is, however, a Miltassia Dark Star. It has about 1/4 Brassia ancestry.
Could this be the parent of what you're growing? Sometimes people don't do the most careful jobs of writing out tags--even some of the best growers in my orchid society are a bit careless and I've had to correct things after trying to look them up.
Interestingly enough, Shooting Star is also not quite all Brassia--only 75%; the rest is Oncidium. So technically it should be Brassidium.
At any rate, if you do, indeed have a cross between Brassidium Shooting Star & Miltassia Dark Star, your plant is an unregistered cross, and a fairly complex one at that. Do you have any photos of the blooms? This way we might be able to confirm or refute this hypothesis. I can provide a list of all the ancestral species and the theoretical proportions in your plant.