Wouldn't it help to keep a few pairs you know are brutal and test those every time? Like light gray on white, dark gray on black, that kind of thing. Your Portland user basically found the worst case for you, so why not bake that case into your checks so it never sneaks past again. Building a fixed set of edge cases sounds way better than just eyeballing whatever happens to be in the file that day. That way you catch the ugly stuff before it hits 2,000 phones, not after some poor person emails you a screenshot. A saved palette of problem colors plus a checker would've saved you that 4 hour rollback.

Man, I feel this in my bones. I've had the same thing happen with those fancy patch kits, the glue always turns into a rock before I even get halfway through it. What finally worked for me was just buying tubes in bulk online, like a 5 pack for cheap, and tossing a spare in my bag so I never get stuck. Yeah it's not as "green" as patching but I got tired of fighting with dried up glue and tiny little patches that peel off after a week. Sometimes the simple answer really does win.