Hello Neb to colour is really easy tobe honest as for getting the correct skin tones is another matter LOL Say you want to colour a face open a image up in
psp make sure its set to 16 mill colour. To do that simply go to colors then into increase color depth. Should be last one in the list. To get a skin tone press Shift key + H together.. Or go to colors at top and go to adjust the go to "hue sat and lightness " Set sat too 51 the hue to 24
the adjust the lightness to get desired face colour.. play around with it you will soon get the face colour your looking for.. Takes time and practice but you will win honest .. Good luck
Regards Barry