Celes Amano Sprite sheet

I'm not terribly familiar with the palette limitations of this game but if I recolored the sprite and used the extended palettes ASM, is there a palette that could approximate these colors?

You can check in FF3usME if one of the first 6 palettes can give a similar result.

If that won't work. What would I need to know about expanding the rom to make this possible?

Palette expansion is a serious headache, because palettes $00-$05 are used for characters but there are more after those use for specific things. You can't just say I'll move the palettes and add one or two at the end, this would require coding inclusions for those palettes. I'm not familiar with the code relevant to overworld and battle paletttes so I can't tell what amount of work this would require.

There's also the SNES limitations, which limit the number of colors on screen and possibly limit the number of palettes used at the same time. I'm not sure if FF6 is close to this limit generally in battle and on map but there must be a good reason why Squaresoft used 6 palettes for 14 characters, I can't believe saving palette space was the only reason.