diff --git a/.todo b/.todo
index ce1ba5d..6cb1134 100644
--- a/.todo
+++ b/.todo
@@ -1,4 +1,3 @@
-document color value ranges
 document 3D coordinate system
 add audio capabilities
 add fillCircle()
diff --git a/doc/index.html b/doc/index.html
index f948076..59493b6 100644
--- a/doc/index.html
+++ b/doc/index.html
@@ -25,6 +25,7 @@ The library functions are documented below.
         <a href="#overview">Overview</a>
         <ul>
             <li><a href="#invocation">Invocation</a></li>
+            <li><a href="#colors">Colors</a></li>
         </ul>
     </li>
     <li>
@@ -59,6 +60,15 @@ The library functions are documented below.
 </ul>
 </p>
 
+<a name="colors" />
+<h3>Colors</h3>
+
+<p>
+Unless otherwise noted, color values described in this document
+consist of red, green, and blue components.
+Each component is a real number that can range from 0.0 to 1.0.
+</p>
+
 <hr />
 
 <a name="ag" />