Ein kleines Manko hat es, es funktioniert nur ab GTK2.
Code: Alles auswählen
procedure TForm1.FormCreate(Sender: TObject);
var
fix, btn, lab: PGtkWidget;
begin
Button1.Width := 150;
fix := PGtkWidget(Button1.Handle);
btn := gtk_bin_get_child(GTK_BIN(fix));
lab := gtk_bin_get_child(GTK_BIN(btn));
gtk_label_set_markup(GTK_LABEL(lab), '<span foreground="red">Rot</span> <span foreground="green">Grün</span> <span foreground="blue">Blau</span>');
end;