When you change the accent color in Windows 10, it will change the color of your Start menu accents, Start button, taskbar, title bars, window borders, buttons, text, Settings accents, sign-in screen accents, and Action Center accents by default. How to Turn On or Off Show Accent Color on Title Bars and Borders in Windows 10
I think it's part of Windows that if you deselect the item, the default is white.
