not bad, I can tell you a basic method for re-coloring sprites.
while zoomed out, decide which area you wish to re-color first (normaly hair)
now zoom in, and look at how many shades (light/dark) are in the area (if doing hair, look at one of the character looking left or right, they have more of a range)
now that you know how many shades to use, decide what color you want (lets say it's red)
go into the color choose, and choose custom color, now move the slide waay down into the darker area of the red
now make "x" ammount of shades of the same color as different custom colors going from light-dark, normally the last 2-3 are reasonbly lighter than the rest
this part will hurt you eyes a bit, zoom in as far as you can go (8x) presumbly, and assuming the original hair color is blue, replace the darkest shade of blue with the darkest shade of red, and so on and so on...
take breaks, cause this will take a while if you re-coloring more than just hair
hoped that helped, btw this is using MS Paint
EDIT: the reason this hurts your eyes, is because it strains them detecting each shade, as some of them are really close in comparison.