That "impossible to scan" line is the whole problem, isn't it. Did you ever figure out what the "one thing" actually was for them? I've found that can be different for every client, even when they all get the same report. Some only care about the budget number, others just want to know if they need to do something this week.

Genius move, I'm totally stealing that trick for my next project.

Does it just find them or does it also explain why they'd work?

Ran into this exact problem on a client site last year. Started bringing my oldest tablet and a cheap prepaid phone to check contrast in real light. Totally agree with @gibson.nathan about testing in harsh conditions. Now I just avoid dark on dark combos completely, even if they look cool in my office. A light gray or white outline can sometimes save a design if you really need those colors. It's not about us, it's about making sure the person on the bus in the sun can actually use the thing.

My refund got delayed three months for the same reason.