You know what? You're right! Skin shader shipped with Houdini doesn't support diffuse colour variation via texture (assuming that Hue Shift is not that thing). This is really odd. Mental ray supports this!
But maybe you can help us to improve it? Jump inside Material (press i) and again in inside Skin Surface Shader you''ll find there. You will see a number vop nodes.
Find a lambert node somewhere close to output. Add Texture VOP and connect it with proper parameters s, t etc (you have there already one texture VOP, so check the example).
Now all you have to do is to multiply lambert output with TextureVOP output and wire it in AddColors VOP.
You need another texture for specular, or to tweak any of your parameter? Proceed in the same way. Add as many textures and operators as you want.
Check available patterns for Vops and ready to use materials accessible via Tab menu. Add, mix, multiply, fresnel, trace them, go ahead, don't limit your self. Free your mind!

Congratulations! You've just made brand new & great SSS shader for Houdini. Share it with us! RMB on Material SHOP, press “Create Digital Asset”. Choose name and new file for it. Upload on Exchange. Be happy.
Now try to do the same thing with mental ray
cheers,
sy.
PS Seriously Houdini's default shaders quality is legendary bad (although they strike to make them much better right now). So if you see something is missing, post a RFE here or, even better, repair it and share with the community!