skin tone paints and xacto knives

I'm looking to expand my customizing skills and try possibly painting some skin tones on my RA figures. Any recommendation as to what brand of paint to use and where to get skin tone paint? The other question I had was I remember seeing customizers use xacto knives to cut heads(to change the mouths of one head to another) and then glue or something to reattach them. Is there any type of xacto knife that anyone would recommend over other brands? And does anyone know a lot about the procedure with the heads I was talking about? Thank you