Updated omitted lengths sentence in section 6.1.

Author: mitp7

css-backgrounds-3/Overview.bs

@@ -2286,7 +2286,7 @@ Animation type: by computed value,
 
   <p>Each shadow is given as a <<shadow>>,
   represented by 2-4 length values, an optional color, and an optional ''box-shadow/inset'' keyword.
-  Omitted lengths are 0; omitted colors default to the value of the 'color' property.
+  Omitted lengths are 0; omitted colors default to currentColor.
   <pre class=prod>
   <dfn><<shadow>></dfn> = <<color>>? &amp;&amp; [<<length>>{2} <<length [0,&infin;]>>? <<length>>?] &amp;&amp; inset?</pre>