On the 'General Information' tab, there is 'Icon colour'.

Right click on folder icon and select 'Properties'.

To choose the outline colour of a folder icon: Or perhaps you might want to select a few special folders that you use more often and give them a different colour. However, the developers also understood that not everyone is going to appreciate a load of icons that all have same monochromatic outline, so they have completely written a bunch of code so allowing people to choose any colour they want, so you could set eg: 'Sent' folder as a green. So as you can see, although I've only mentioned a few important considerations, there is a lot to consider when choosing something as simple as an icon. They are also designed to cope with those who require good contrast or suffer from colour blindness issues. SVG graphics do not lose any quality if they are zoomed or resized, so you can understand how this would benefit many people with different requirements. These new icons are Scalable Vector Graphics commonly called SVG.

The new icons are called Photon icons which only come with an outline. So a new solution that provided scalable icons which operated for contrast requirements and could offer personalised colouration was required. It is understandable that trying to use Thunderbird with a blurry icon issue is not exactly providing a product that is inclusive for all people. For others the icons were a predefined colour which some found almost invisible. Not everyone has the same screen resolution nor same monitor size nor same eyesight and the old folder icons were PNG images which were not scalable and for some people this caused issues and the icons became blurry. Some info to help explain what has been going on behind the scenes in developer land and why they were put into the position of finding a new solution.

Change default folder color mac