In CC3.3, I use headshot pro to create a character. At first the color of the head (except the face) is the same as the rest of the body.
Then, I fine tune morphs using 'activate image matching tool' and Re-Project Photo. No masks on. And repeat several times.
So far the body color is consistent with the head:


Then, I add a face mask (default even) with or without eyelid mask. In this step, somehow the color of the body neck and below becomes distinctly different from the head. I don't know why but this has happened to me several times now. 


I try manually changing 'Skin Color' to match the body color to the face, which is successful,
but then the head color (except face) becomes too different from the face/body color as follows:


Is this because I use an Asian photo in headshot?
Or is there some other reason for this?

In any case, please teach me how to get around this color mismatching problem.
Thanks in advance.

It looks like a bug. The ethnicity of the source photo shouldn't matter. 

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Thanks for the quick response. 
If it's a bug regardless of ethnicity, how come no one has yet to point this out? (I couldn't find any post on this matter!)
Were you aware of this bug?

The "Skin Color" in Headshot does deal with the skin of the head (except face) and the body.
In headshot, go make any changes to the skin color and you'll see what I mean.
The skin color adjustment is in the headshot in order for you to change the skin color of the body and head (except face) when you happen to modify the face skin color in headshot. 
So the unintended change of the skin color of the body (but not the head) while you're still working on the headshot is defeating the purpose of having "skin color" adjustment of body and head (except face).

I'm currently experimenting to see exactly when the skin color of the body erroneously changes as shown in my second picture above. 
Originally when I posted the question, I thought it changed right after I added the face mask. But I was wrong about that.
It changed only after I edited the Photo Diffuse file on Photoshop and updated Skin Texture.
(Editing Blend Mask doesn't seem to change the color of the body skin!)


Appearance Editor cannot rectify this error, because in CC3+ the head skin includes neck as well as the head (and face).
As shown in my second picture above, the problem lies in the fact that the skin color of the neck becomes different from that of the head.
Changing the skin color of the head in Appearance Editor will only change the head AND neck at the same time.

I stand corrected.
The culprit is not the Photo Diffuse editing. 
It's "Update Skin Texture". 
The worst part is the color change is random.
Sometimes the color of the body (neck and below) doesn't change after several times you "update skin texture" with adding masks, but if you repeatedly "update skin texture" with different masks, the color does change even though you don't even touch Photo Diffuse.

VRTeacher, this has been mentioned forums already, I myself have brought this up in the CC 3.3 Technical issues post

https://forum.reallusion.com/FindPost452729.aspx

https://forum.reallusion.com/FindPost453371.aspx

It seems it has to do with the "old CC3 head" and the "old CC3 body" now having been joined in a single head map with the neck now being a part of the head map, and a saturation bug.

  
But to 4u2ges point, do not hesitate to post and report your findings in the Feedback Tracker.  It will help RL track the progress of outstanding issues.  Also, others may have found their own workarounds or just are too lazy to post in Feedback Tracker if they found it does not matter so much.  So if you do care, then you can always make the Feedback Tracker post yourself, and then share that Feedback Tracker post with the forum, like 4u2ges did.   

It seems this "bug" still persists in CC4.21 see traker issue Issue 9418 from mar/apr 2023

Let me give you my take on the issue.
They partially fixed the original issue in CC3. The color replacement issue was never fixed though and is still not working right.
God forbid to make any (not to mention radical) changes for skin color in Headshot panel.
Head/Neck color discrepancy would be accumulating with each color change, seam would become distinct and eventually body texture would become washed out.
That is the reason I never touch this control in Headshot.

I tell you more. Head/Neck color most never blend right even for freshly generated head before making any changes.

I usually use color replacement brush in Photoshop to match face tint with the neck, or neck with the face.
In latter case I use the same brush and paint all other body textures. It is simple and effective way to match/blend.


And if I need to change the overall skin tint I would do it in DHS skin color tool or in Appearance Editor with Base Color controls.