diff --git a/PIL/ImageColor.py b/PIL/ImageColor.py
index fc95e6d19..56c38e419 100644
--- a/PIL/ImageColor.py
+++ b/PIL/ImageColor.py
@@ -126,7 +126,7 @@ def getcolor(color, mode):
     return color
 
 colormap = {
-    # X11 colour table (from "CSS3 module: Color working draft"), with
+    # X11 colour table from https://drafts.csswg.org/css-color-4/, with
     # gray/grey spelling issues fixed.  This is a superset of HTML 4.0
     # colour names used in CSS 1.
     "aliceblue": "#f0f8ff",
@@ -248,6 +248,7 @@ colormap = {
     "plum": "#dda0dd",
     "powderblue": "#b0e0e6",
     "purple": "#800080",
+    "rebeccapurple": "#663399",
     "red": "#ff0000",
     "rosybrown": "#bc8f8f",
     "royalblue": "#4169e1",