(2 ratings)
Not the highlight - blend it's right yellowish with some touch of blue - it will make a sense of depth. Yep for ice\fire or any you can attach them here (if they have similar shape concept).
Although nicely drawn already, in my own perspective of usefulness it's really hard to imagine how a bunch of bones are related to abilities or tech-tree upgrade.
You could try focusing in one way, making it to looks like a proper item with darker background and different variations like one bone, few bones and finally this.
Similar suggestion can be applied on tech-tree ones.
If you insist going on ability, trying replacing some bones with better effect like dark runes or whatever it fits.