When you first apply the G3F genitalia to a G3F based character it will have no skin texture and usually looks grey.  With G1 and G2F the genitalia also looked grey when you applied it, but you could just apply the normal full skin mat for the character to the genitalia and it would be textured. With G3F this is no longer true. As Richard Haseltine indicated, the G3F genitalia has its own UVs and needs its own textures. V7 herself comes with textures for the genitalia, at least in the pro bundle that includes the genitalia, and so do the other characters that were included in the pro bundle. 

Not all G3F/V7 characters, however, include genitalia textures. You have to read the description of what is included carefully and if they do not mention a genitalia texture, it probably is not included. Some PAs have included a genitalia morph instead of a texture. This morph applies to G3F without the genitalia add on and is probably good enough for artistic renders, but not for hard core porn.

Some PAs have indicated that they are not doing genitalia textures because they include tattoo options and the genitalia with is own UVs makes doing the tattoos very difficult if the tattoo crosses the boundary.