Just as a heads up, the HazCams on Perseverance are in fact in color (Source: https://link.springer.com/article/10.1007/s11214-020-00765-9 - "The Mars 2020 Navcams and Hazcams offer three primary improvements over MER and MSL. The first improvement is an upgrade to a detector with 3-channel, red/green/blue (RGB) color capability that will enable better contextual imaging capabilities than the previous engineering cameras, which only had a black/white capability.") Your observations are correct though - the stereo precision is important, so there was additional analysis of the stereo depth computation to make sure it wouldn't cause an issue.