In MDL-83639 some custom icons were added to core because FontAwesome couldn't cover the needs (See attachment).

A very important difference between FontAwesome icons and these custom SVGs is that FA is a font that can be easily coloured (also by Bootstrap), but colouring SVGs is not that straightforward. Because of this, there are some inconsistencies in the current UI

Or, in this situation, the need to add the same SVG icon with different colours to accomplish the "hover" styling: https://github.com/moodle/moodle/tree/main/ai/placement/courseassist/pix

We should find a solution to cover our icon needs and be able to easily colourize them, being displayed in a homogenised way. Some exceptions to this could be icons that are used in a specific scenario and don't need flexible colourizing (icons for zero states, ...).