In Stellaris, my fleets' firepower amounts are listed under their location in the Outliner window in yellow. I assume this is the default font color for the UI.
However, one of my fleet's firepower label is listed in red, and there's no indicator or tooltip explaining the difference in color. I don't think the guided tutorial slave robot covered this, either.
Why is one of my fleet's firepower labels showing up as red?
To provide a bit more information, my 3rd Fleet is comprised of 14 Corvettes. My 1st Fleet, by comparison, has 12 Corvettes and 1 Cruiser. I don't recall the ship breakdown of my 2nd Fleet at the moment.
Originally, I surmised that the red color coding was because my 3rd Fleet was executing a combat order/was in combat, but I saw the red number even when the relevant fleet was not in combat or heading toward combat, which rules out that theory.
Best Answer
The red fleet power number is telling you that the fleet in its current state is significantly below the power of its template in the Fleet Manager. This can be because either the fleet needs upgrading or reinforcing. The Up arrow to the left of the fleet power indicates that you could use an upgrade.
Your "1st Fleet" on the other hand can also use an upgrade, but as its 14 size is greater than its template's size "(13)", its fleet power is at least that of its template.
I'd need to see more information to explain why your "2nd Fleet" of size 13 has at least the fleet power of its size 15 template.
The new Fleet Manager is a very cool tool. I definitely recommend you get comfortable using it.