Hot take: a gray scale print test saved me 2 hours on a client's chart last month
I kept tweaking the red and green lines on a stacked bar chart for a client in Denver because I could not tell them apart in the mockup, and I finally printed the whole thing in grayscale after 2 hours of guessing. Turns out the two colors had nearly the same brightness, so I added different hatch patterns to each bar and the whole thing read fine for my colorblind coworker. If you have a quick way to check contrast between similar shades, what do you use?