examples: fill hex field with black

examples/lib/colorspace.html

@@ -7,7 +7,7 @@
     <h1>Color Space Converter</h1>
     <div id="hex">
       <label><code>HEX:</code></label>
-      <input type="text" id="hex-str">
+      <input type="text" id="hex-str" value="#000000">
     </div>
     <div id="rgb">
       <label><code>RGB:</code></label>