I personally run HIGH CONTRAST (varies OS by OS) and am butting heads with a few sites, and an increasing number, which don't play fair. Browser is set to reject all font/color/size, the OS is limited to a 16 color palette, and (this is different) JS turned OFF...
Do you acknowledge those with visual difficulties, have their down desired font choice/size?
Are you missing business, ... or ignore a segment of the web with actual cash for those who drive up numbers with no conversions?
The above is a rant, dismiss that. The real question is "Does your site render properly in High Contrast: for accessibility purposes?"
Do you test it in your dev systems? (easy to do, question is do you do it?)
The web is a great big vibrant place ... but it started with some who are now aging and that number is increasing day by day. Do you remember them in your coding?
Just wondering. These days I check it out both ways (I am 70) just to make sure. Serve all is my motto. And KISS (Keep It Simple Stup... er... substitute your favorite pronoun)