Undefined index warning when changing colours

There's a problem with our color module support.

Changing to a preset gets this warning:

# Notice: Undefined index: base in _color_rewrite_stylesheet() (line 438 of /Users/joachim/Sites/7-drupal/modules/color/color.module).

The reason is this in color.module:

  $base = 'base';
// ... SNIP
      if ($key = array_search($chunk, $default)) {
        $chunk = $conversion[$key];
      }
      // Not a pre-set color. Extrapolate from the base.
      else {
        $chunk = _color_shift($palette[$base], $default[$base], $chunk, $info['blend_target']);
      }

So basically, it looks like 'base' must be a defined color in a scheme -- it's hardcoded into colour module.