Fixes a few RPD painting bugs

Changes RPD colors to be consistent with pipe painter & default pipes.
Makes the RPD properly update its neighbors on painting.
Offloads the neighbor updating logic from pipe_painter to a pipe proc.
Fixes #6783

code/ATMOSPHERICS/pipes.dm

@@ -49,4 +49,8 @@
 			var/obj/item/pipe_meter/PM = new (T)
 			meter.transfer_fingerprints_to(PM)
 			qdel(meter)
-	..()
+	..()
+
+/obj/machinery/atmospherics/pipe/proc/update_node_icon()
+	//Used for pipe painting. Overriden in the children.
+	return

code/ATMOSPHERICS/pipes/manifold.dm

@@ -115,6 +115,15 @@
 /obj/machinery/atmospherics/pipe/manifold/pipeline_expansion()
 	return list(node1, node2, node3)
 
+/obj/machinery/atmospherics/pipe/manifold/update_node_icon()
+	..()
+	if(node1)
+		node1.update_icon()
+	if(node2)
+		node2.update_icon()
+	if(node3)
+		node3.update_icon()
+
 
 //Colored pipes, use these for mapping
 /obj/machinery/atmospherics/pipe/manifold/general

code/ATMOSPHERICS/pipes/manifold4w.dm

@@ -122,6 +122,17 @@
 	if(node4)
 		overlays += getpipeimage('icons/obj/atmospherics/pipe_manifold.dmi', "manifold_full[invis]", WEST)
 
+/obj/machinery/atmospherics/pipe/manifold4w/update_node_icon()
+	..()
+	if(node1)
+		node1.update_icon()
+	if(node2)
+		node2.update_icon()
+	if(node3)
+		node3.update_icon()
+	if(node4)
+		node4.update_icon()
+
 //Colored pipes, use these for mapping
 /obj/machinery/atmospherics/pipe/manifold4w/general
 	name="pipe"

code/ATMOSPHERICS/pipes/simple.dm

@@ -137,6 +137,13 @@ The regular pipe you see everywhere, including bent ones.
 /obj/machinery/atmospherics/pipe/simple/pipeline_expansion()
 	return list(node1, node2)
 
+/obj/machinery/atmospherics/pipe/simple/update_node_icon()
+	..()
+	if(node1)
+		node1.update_icon()
+	if(node2)
+		node2.update_icon()
+
 /obj/machinery/atmospherics/pipe/simple/insulated
 	icon = 'icons/obj/atmospherics/red_pipe.dmi'
 	icon_state = "intact"