I created a female character using Headshot 2.0.  Made some adjustments via SkinGen as well.
I was able to match up the skin tones between head and body.  Looks great.
I then create her a man to call her own.  Also using Headshot 2.0 and making some adjustments via SkinGen.
However, this guy will not let me match his head and body color.  I've tried everything I know and several things I didn't know and a couple of things I made up as I went.
Nothing works. 
Comparing projects, I noticed the Base Color Maps were completely different.  I'm not sure how they got changed for the female (or maybe they changed for the male but I don't think so).
Any ideas on how to fix the male's neck line?  Any info that would help me understand why the Base Color Maps are so different would be appreciated as well.
Female Head:


Female Body:



Female Result (no neck line):


Male Head:


Male Body:


Male Result (clear neck line):

For the female you have a flat color texture and it matches because it's the same and even at UV seams.
The male has a base darkened texture and it varies at the seams - thus seams are visible.

Easy way is just to open all base color textures in Photoshop or some other image editor and paint over the seams/edges with the same color using a soft brush.




And it will match just fine



It's better to open and save textures from within skingen editor. Otherwise next time you go to skin editor all your layer would be flatten.

The other way to fix that is to use 3D paint tools such as 3D Coat. It's not hard, just need to have it at the disposal.