allow replacement nodes during airbrushing

API.md

@@ -13,6 +13,7 @@ minetest.register_node("mymod:colored_node", {
 	palette = "unifieddyes_palette_extended.png",
 	groups = {snappy = 1, cracky = 2, ud_param2_colorable = 1}
 	on_construct = unifieddyes.on_construct,
+	airbrush_replacement_node = "mymod:my_other_colored_node"
 })
 ```
 
@@ -31,6 +32,8 @@ minetest.register_node("mymod:colored_node", {
 
 `on_construct`: see below.
 
+`airbrush_replacement_node`:  The node to swap in when the airbrush is used on this node.  For example, you could `minetest.override_item()` on some default node to add this field, pointing to a colorable node of your own, so that when the default node is painted, it's replaced with yours in the new color.
+
 #### Function calls
 
 **`unifieddyes.fix_rotation(pos, placer, itemstack, pointed_thing)`

init.lua

@@ -633,7 +633,7 @@ function unifieddyes.getpaletteidx(color, palette_type)
 	end
 end
 
--- punch-to-recolor
+-- punch-to-recolor using the airbrush
 
 function unifieddyes.on_airbrush(itemstack, player, pointed_thing)
 	local player_name = player:get_player_name()
@@ -691,7 +691,9 @@ function unifieddyes.on_airbrush(itemstack, player, pointed_thing)
 		return
 	end
 
-	minetest.swap_node(pos, {name = node.name, param2 = fdir + idx})
+	local name = def.airbrush_replacement_node or node.name
+
+	minetest.swap_node(pos, {name = name, param2 = fdir + idx})
 	if not creative or not creative.is_enabled_for(player_name) then
 		inv:remove_item("main", painting_with)
 		return