A função color-theme-billw usa internamente a função color-theme-install-frame-params para alterar os parâmetros do quadro. Assim, você pode alterar os parâmetros do quadro da mesma maneira:
(require 'color-theme)
(color-theme-initialize)
(color-theme-billw)
(color-theme-install-frame-params
'((background-color . "gray12")))
C-h f color-theme-install-frame-params
(color-theme-install-frame-params PARAMS)Change frame parameters using alist
PARAMETERS.If
color-theme-is-globalis non-nil, all frames are modified usingmodify-frame-parametersand thePARAMETERSare prepended todefault-frame-alist. The value ofinitial-frame-alistis not modified. Ifcolor-theme-is-globalis nil, only the selected frame is modified. Ifcolor-theme-is-cumulativeis nil, the frame parameters are restored fromcolor-theme-original-frame-alist.If the current frame parameters have a parameter
minibufferwith valueonly, then the frame parameters are not installed, since this indicates a dedicated minibuffer frame.