Cutting the collar is not always the killer people make it out to be, plenty of old timers flush cut everything and their trees live just fine. Thick bark makes the collar hard to see but you can feel the ridge with your thumb before you ever pull the saw out. Maybe the real problem in Reno was the maple was already too far gone and the cuts just got the blame.

Read a thing a while back about how contrast ratios came from actual research on how well people can read text, not just someone's opinion. Your boss's fancy monitor probably has better brightness and color than 90% of the screens your users are staring at. Trust the numbers because the numbers don't care about your office lighting. When a client digs in on their brand color, I'd show them the failing score and then offer a darker or lighter shade of that same color that still passes. Nine times out of ten they never even notice the difference once it's on the page. Their brand can stay, it just needs a tweak so actual humans can read it.