Icons' color does not change with the theme

The colors of the UI icons are only set to work with the default light/ dark theme of Brave. When I install a theme from Chrome Web Store or even ThemeBeta, all colors change, except the icons.


Description of the issue:
How can this issue be reproduced?

Expected result:

Brave Version( check About Brave):
1.5.115 (Windows 10)

Additional Information:

unnamed
This is how the theme should work

Screenshot_1
This is how it actually works (using default light theme)

Screenshot_2
This is how it actually works (using default dark theme)