

If I can recall the vid I watched on GIMP 3, the whole UI is now customizable with CSS. You could dive a bit into it and see if you can change out or recolor the icons (recoloring should be doable if they’re SVG, but you might need to decode base64, change the color and recode it into base64).
However, it shouldn’t be too long before custom UIs start pouring out. So if CSS isn’t your thing, keep checking back and see if someone has made something that ticks all your boxes!
Wait wait. I just found something. Head to Edit > Preferences > Icon Theme and switch to Legacy.
And bam. Gimp 3 is out, though! Should already be updated if your system is up to date!