I had a stroke reading that... Sorry dude.
But from what I understood, I'd answer that the main goal is for each icon to be readable. As you can see, they're already quite small... So adding the "prestige flair" would probably make a big mess of colors.
It's a small thing, I agree, but I'd also think that you probably know which perks have been prestiged, no? It's honestly not a big deal to simply click on it and see !