You must select the Genesis 3/8 figure, load the Dicktator graft, then copy the mats, then load the shell, and Then Select the shell and load a texture set.
I don't know what you mean by the head is darker, if you mean the shaft, then that comes from the texture set you loaded on the shell. Dicktator comes with basic texture sets, and they don't cover many skin tones.
If you want more choices/skin tones, grab Texture Wizard from here :
https://f95zone.to/threads/texture-wizard-2019-12.21464/
It adds a bunch of texture sets for the shell, as well as more veins effects, and wet effects.
There is also guide to help with different things converning Dicktator here as well :
https://f95zone.to/threads/guide-dicktator-with-texture-wizard-mod-using-wet-maps.47828/