Tested on several monitors, different pc, different sites, themes, always there. Not a problem in Chrome or Edge. Will be a different color at times for reasons unknown... maybe doesn't happen all the time (maybe it does but when it's black it's impossible to see)

Can't really see it in the fullscreen pic with a white background here, but it's there as I see it... get it on a dark background and it's fairly obvious (well, as obvious as a single blue pixel can be). Added second more obvious windowed pic.