How to change font/background color of svg icons ?

svg icons are usually transparent, and have a stroke color.

Try https://tablericons.com/icon/ad

set the color and background in the containing element

Since your project uses Bootstrap, you can enhance it by including the Bootstrap Icons library. To customize the icon colors, use the provided sprite and apply a .text-* class or custom CSS for color styling. For example:

<svg class="bi bi-exclamation-triangle text-success" width="32" height="32" fill="currentColor" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
  ...
</svg>

This approach allows you to easily adjust the icon's appearance while keeping your design consistent with Bootstrap's styling conventions.

Or, you can follow the solution proposed by @snapey and modify the fill and stroke attributes directly.