[Graphics] Is it safe to change the 7 row palette?

I change the Tileset of the map, but I noticed that the 7th row(advance map) of paint is mostly filled with emptiness. What is it connected with?

Maybe it took some space to make room somewhere else?

In my experience, it seems that palette 7 is linked with the secondary tileset, but never used. Therefore, it kind of has that feeling of being "dynamic", in the sense that, you can use palette 7 for either the main or secondary tileset and not have issues. I've done that, and I have never run into any issues with it

Yeah, I like to use these for tiles in the primary tileset when I want the palette to change according to the secondary tileset. Haven't had issues with it before =)