Celes Amano Sprite sheet

There are a total of 8 ($00-$07) actor palettes. These are "permanently" loaded during overworld/town. They can be edited in real-time, such as with pallete $06 which is used for special situations and is changed from scene to scene depending on what extra sprites are needed (such as Esper Terra or explosion graphics). $07 works similarly, but is reserved for things like the chocobo and magitek sprites. $00-$05 are the standard PC/NPC palettes and can't be changed without altering a lot of common sprites. Technically you can change them just like $06-$07, but again, there are a lot of sprites that use them so it would mean changing a lot of NPCs if this is for a PC palette change.

Battle is much cleaner, each character gets a unique palette (as far as memory is concerned), by default there is only palettes $00-$06 (a different$06), however with ASM you can expand this to as many as you want. The reason this is the case is that you only get 4 characters in battle, so there is enough VRAM for each character to get its own. Plus they don't "share" palette space due to status effects that temporarily alter the pallete for one person at a time.

The only other key difference between overworld and battle palette usage is the color limit. In the overworld, you get the full 16 colors to work with (15 + 1 transparent). In battle you are restricted to only 12 (11 + 1). But, by expanding the battle palettes the way I mentioned above, you can actually use any 12 colors (11 + 1) for your sprite and have a separate sprite/palette load for battle. This allows a much wider range of color usage in your PC sprites without being tied to Vanilla PC restrictions.

I might have a video on this somewhere... I'm not sure. I will look into it and get back to you if this interests you.