Where is this mysterious color scheme override coming from?

Note that question involves a plugin, but I don't think the plugin is fundamentally relevant. 

I installed the Gruvbox Theme plugin into GoLand, and one of the things it does is install editor some corresponding editor color schemes. However, I found that the color scheme used for Go, the language, has some oddities. 

I went to investigate, and found that a number of the syntax elements' colors for Go had overrides from the Language Defaults. Here's an example:

I was surprised to see what appeared to be a Go-specific override in this generic color scheme, so I went to examine the color scheme's source, searching for the hex color C7773E. To my surprise, the string "777" doesn't appear in that color scheme at all! Every option relating to a keyword is set to the color I'm expecting, FB4934.

I figured I must have missed something, so I also exported this color scheme from GoLand directly, and examined the .icls XML file. Again, "777" is nowhere to be found, and again, every option related to keywords is set to FB4934. I re-imported this file unchanged, and examined it in the GoLand UI — once again, the color was overridden for Go!

Finally, I simply changed the color scheme by enabling "Inherit values from:", like this:

This works, but the UI indicates I've changed the color scheme from its default, which I don't understand, given that the scheme itself doesn't seem to have the C7773E color at all.

So, what is going on? Where is the C7773E color override coming from, if it's not in the color scheme?