Why I can not change tab color in GUI?

[chjie7]

I can hardly read the filename on tab w/ default colors (grey), so I change it as below:

hi TabLineSel ctermfg=220 ctermbg=33 guifg=Yellow guibg=#0037BD "Yellow on Cobalt

It works under terminal (Linux or Mac), but Gui of MacVim does not change color. (So do TabLine and TabLineFill)

Could anybody help explain what's the problem?

(Env: Vim 8.2 on macOS 10.11.6 and 12.3)