when setting background color, use allocated color, and don't overwrite with bg of None
when setting background color, use allocated color, and don't overwrite with bg of None

rvu95/vte,pjm0616/vte,gloob/vte-copy,rvu95/vte,saitoha/vte-sixel,flaxandteal/gasket-vte,flaxandteal/gasket-vte,asivokon/vte-fx,saitoha/vte-sixel,saitoha/vte-sixel,jessevdk/vte,aligo/vte,asivokon/vte-fx,gloob/vte-copy,flaxandteal/gasket-vte,jessevdk/vte,rvu95/vte,thestinger/vte-ng,asivokon/vte-fx,aligo/vte,thestinger/vte-ng,thestinger/vte-ng,jessevdk/vte,rvu95/vte,flaxandteal/gasket-vte,jessevdk/vte,asivokon/vte-fx,pjm0616/vte,pjm0616/vte,gloob/vte-copy,aligo/vte