The Colored Master Category Row setting is fairly self-explanatory.
If the larger, bolder text and the accordion collapse/expand arrow aren’t obvious enough indicators, you might like this setting. It changes the color of the Category Group headings to make them even more obvious — that is, if you use the Default theme.
If you use the Dark theme, the “colored” rows are much less obvious. And if you use the Classic theme you’re completely out of luck. No colored Category Group headings for you!
[*For those who never used an earlier version of YNAB, a Master Category is what’s now referred to as Category Group.]