A skin ramp takes a skin colour down into warm, slightly red shadows and up toward a paler, more yellow highlight. Below are ramps for pale, mid and dark skin.
Basecoat the skin, shade the creases (eye sockets, under the nose and chin, between fingers), then highlight the brow, cheekbones, nose and knuckles, smaller with each step.
Each ramp below is built the way the Ramps mode on the colour wheel builds one: we set a target colour for each step, then pick the nearest opaque paint in each brand (no metallics, washes or contrast paints, and no paint used twice). ΔE says how far each paint is from its target: close is under 6, fair under 12. Swatch colours are estimates, so test the ramp on a spare model first. On the wheel you can build the same ramp from any paint, or only from the paints you own.
Target ramp (darkest to lightest):
Closest fit overall: Army Painter (average ΔE 5.3 per step).
Target ramp (darkest to lightest):
Closest fit overall: Citadel / Warhammer (average ΔE 4.7 per step).
Target ramp (darkest to lightest):
Closest fit overall: AK Interactive (average ΔE 4.5 per step).