diff --git a/src/p_setup.c b/src/p_setup.c
index b26459759..56ed06a66 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -1466,6 +1466,7 @@ static void P_LoadRawSideDefs2(void *data)
 		{
 			case 63: // variable colormap via 242 linedef
 			case 606: //SoM: 4/4/2000: Just colormap transfer
+			case 447: // Change colormap of tagged sectors! -- Monster Iestyn 14/06/18
 			case 455: // Fade colormaps! mazmazz 9/12/2018 (:flag_us:)
 				// SoM: R_CreateColormap will only create a colormap in software mode...
 				// Perhaps we should just call it instead of doing the calculations here.
diff --git a/src/p_spec.c b/src/p_spec.c
index e20d85af6..7d6ffaf2a 100644
--- a/src/p_spec.c
+++ b/src/p_spec.c
@@ -3253,6 +3253,63 @@ static void P_ProcessLineSpecial(line_t *line, mobj_t *mo, sector_t *callsec)
 			}
 			break;
 
+		case 447: // Change colormap of tagged sectors!
+			// Basically this special applies a colormap to the tagged sectors, just like 606 (the colormap linedef)
+			// Except it is activated by linedef executor, not level load
+			// This could even override existing colormaps I believe
+			// -- Monster Iestyn 14/06/18
+			for (secnum = -1; (secnum = P_FindSectorFromLineTag(line, secnum)) >= 0 ;)
+			{
+				if (line->flags & ML_EFFECT3) // relative calc
+				{
+					extracolormap_t *exc = R_AddColormaps(
+						(line->flags & ML_TFERLINE) ? line->backsector->extra_colormap : sectors[secnum].extra_colormap, // use back colormap instead of target sector
+						line->frontsector->extra_colormap,
+						line->flags & ML_EFFECT1,  // subtract R
+						line->flags & ML_NOCLIMB,  // subtract G
+						line->flags & ML_EFFECT2,  // subtract B
+						false,                     // subtract A (no flag for this, just pass negative alpha)
+						line->flags & ML_EFFECT1,  // subtract FadeR
+						line->flags & ML_NOCLIMB,  // subtract FadeG
+						line->flags & ML_EFFECT2,  // subtract FadeB
+						false,                     // subtract FadeA (no flag for this, just pass negative alpha)
+						false,                     // subtract FadeStart (we ran out of flags)
+						false,                     // subtract FadeEnd (we ran out of flags)
+						false,                     // ignore Fog (we ran out of flags)
+						line->flags & ML_DONTPEGBOTTOM,
+						(line->flags & ML_DONTPEGBOTTOM) ? (sides[line->sidenum[0]].textureoffset >> FRACBITS) : 0,
+						(line->flags & ML_DONTPEGBOTTOM) ? (sides[line->sidenum[0]].rowoffset >> FRACBITS) : 0,
+						false);
+
+					if (!(sectors[secnum].extra_colormap = R_GetColormapFromList(exc)))
+					{
+						exc->colormap = R_CreateLightTable(exc);
+						R_AddColormapToList(exc);
+						sectors[secnum].extra_colormap = exc;
+					}
+					else
+						Z_Free(exc);
+				}
+				else if (line->flags & ML_DONTPEGBOTTOM) // alternate alpha (by texture offsets)
+				{
+					extracolormap_t *exc = R_CopyColormap(line->frontsector->extra_colormap, false);
+					exc->rgba = R_GetRgbaRGB(exc->rgba) + R_PutRgbaA(max(min(sides[line->sidenum[0]].textureoffset >> FRACBITS, 25), 0));
+					exc->fadergba = R_GetRgbaRGB(exc->fadergba) + R_PutRgbaA(max(min(sides[line->sidenum[0]].rowoffset >> FRACBITS, 25), 0));
+
+					if (!(sectors[secnum].extra_colormap = R_GetColormapFromList(exc)))
+					{
+						exc->colormap = R_CreateLightTable(exc);
+						R_AddColormapToList(exc);
+						sectors[secnum].extra_colormap = exc;
+					}
+					else
+						Z_Free(exc);
+				}
+				else
+					sectors[secnum].extra_colormap = line->frontsector->extra_colormap;
+			}
+			break;
+
 		case 448: // Change skybox viewpoint/centerpoint
 			if ((mo && mo->player && P_IsLocalPlayer(mo->player)) || (line->flags & ML_NOCLIMB))
 			{