Separate the usual rgbgfx flags from the --color specification

Makefile

@@ -209,15 +209,19 @@ gfx/pokemon/girafarig/front.animated.tilemap: gfx/pokemon/girafarig/front.2bpp g
 
 ### Pokemon and trainer sprite rules
 
+gfx/pokemon/%/back.2bpp: rgbgfx += --columns
+
+gfx/trainers/%.2bpp: rgbgfx += --columns
+
 gfx/pokemon/%/back.2bpp: gfx/pokemon/%/back.png gfx/pokemon/%/normal.gbcpal
-	$(RGBGFX) --columns --colors gbc:$(word 2,$^) -o $@ $<
+	$(RGBGFX) $(rgbgfx) --colors gbc:$(word 2,$^) -o $@ $<
 gfx/pokemon/%/front.2bpp: gfx/pokemon/%/front.png gfx/pokemon/%/normal.gbcpal
-	$(RGBGFX) --colors gbc:$(word 2,$^) -o $@ $<
+	$(RGBGFX) $(rgbgfx) --colors gbc:$(word 2,$^) -o $@ $<
 gfx/pokemon/%/normal.gbcpal: gfx/pokemon/%/front.gbcpal gfx/pokemon/%/back.gbcpal
 	tools/gbcpal $(tools/gbcpal) $@ $^
 
 gfx/trainers/%.2bpp: gfx/trainers/%.png gfx/trainers/%.gbcpal
-	$(RGBGFX) --columns --colors gbc:$(word 2,$^) -o $@ $<
+	$(RGBGFX) $(rgbgfx) --colors gbc:$(word 2,$^) -o $@ $<
 
 
 ### Rules to match specific Pokemon and trainer sprites