My follower's body has mismatched color.
So, I used a different kind of companion mod. This error didn't happen in one companion mod, but happened in all companion body mod.
I used CBBE body, and downloaded all the mod requirements (all follower/companion requirements).
The face didn't turn to purple, but the body turned to light grey or something. The bug happened when I changed my companion's outfit. When there's a sunlight, the body glows as well. I have all the DLCs.
Here's a screenshot of the bug / error :