In Daz, this technique is referred to as the "diffuse tan". You can make an existing skin texture that is presumably fair skinned look more tanned, but it takes a proper choice of which direction you "push" the texture. You would want the slider for shade somewhere between red and yellow, then play with the little square in the color box. The further down you drag it, the darker things get. The further to the right, the more like the color on the color shade slider. You can only push a texture toward tanned so much before it starts looking fake. This is what I call the "spray painted" look. In particular, the palms and soles of the feet will look too dark. You can get skin textures that look tanned. You can also get decal sets that add tan lines.