The red stars must bee more (over)stable than others. My yellow TEEREX 175 and the orange TEE-REX 175 are less stable than the red TEE-REX 174. It`s the same with teebirds.
I love red star teerex's. If I remember correctly back when they first came out I read that the red was more overstable because darker colors take longer to cool so the top of the disc sinks more. I have a white and a red in the same weight almost the same age and they are two completely different discs. They are both great discs so the difference in stablility has worked well for me.