What do the blue colored skill icons indicate?

Solution 1:

I try to write this without any spoilers, but it is a bit hard. If you haven't finished the game yet, proceed at own risk.

I noticed it too and couldn't find any correlation and just brushed it off as nothing special. After seeing your question here I started the game again and went to the skills menu. Note that I finished the game and got every single skills unlocked.

There are a few things to notice:

• Through the Shadow of War main game and Blade of Galadriel DLC the upgrades Domination and Packmaster are the only blue icon's. For the Baranor DLC there are other icons blue, but it is meant to bring distinction between characters and it is quite obvious it has nothing to do with the skill itself.
• The two upgrades are always blue, whether they are active or not.
• The upgrades both are relevant to domination (orc's and caragors)
• Blue is the color of the wraith celebrimbor
• Packmaster doens't seem to work anymore in the final act
• Domination isn't exactly the same anymore in the final act, but overal it still does roughly the same thing.
• All other domination skills stay the same in the final act
• The same icon for Domination is used in white for Raise Dead -> Undying Loyalty (final act)
• Other related (non-blue) skills:
  • Ground finisher - Ground drain: This might use the same action, but is not based on domination, but rather on drain. If you disable the Domination upgrade, this upgrade still does what it should do.
  • Deadly Spectre - Spirit Drain: Same story as ground drain, can still be used with Domination disabled.
  • Shadow Strike - Shadow Dominate: This is an odd one, it still works with Domination upgrade disabled and is the only way to dominate an orc or (broken) beast with Domination disabled.
  • Dominate Captain: This skill does not depend on the Domination upgrade and once you complete the related quest, you can always dominate captains.

I tested the Packmaster upgrade multiple times with multiple (broken) caragors in the final act but I always ended up with 1 caragor, can somebody confirm? If this holds, the blue color seems to suggest that the original functioning is tied to Celebrimbor and might be changed in the final act. The color difference in icon with Undying Loyalty could explain this.

I know this isn't hard proof but is is the closest I could come. IF anyone has some suggestions, feel welcome to post them in comments.

Solution 2:

According to steam's forums and reddit the blue skills are unlocked as part of story progression and white skills are unlocked via points.

This means, Packmaster and Domination are story-provided skills whereas the rest are player-build choices.