i got confused because very many skins use the color returned by Setting_GetSkinElementColor(2,...) in many places. i think that Setting_GetSkinElementColor(2,...) actually returns the generic background color of buttons. it's a useful color because it can't be auto-generated from other available colors, so please leave it as is. (Btw, does Setting_GetSkinElementColor(2,...) return the correct foreground color either? most skins use similar foreground colors in many places, so it's hard to find out it myself). anyway, thank you very much.
but what i meant by "skin accent color" in the OP is button background
mouseover color (foreground mouseover color would be helpful too). this color is frequently used as a
selected menu item background too (but it seems that not always; this might depend on the skin). see screenshot: