code: public static boolean isRGBColorValue (@Nullable final String sValue)
    {
      final String sRealValue = StringHelper.trim (sValue);
      // startsWith as speedup
      return StringHelper.hasText (sRealValue) &&
             sRealValue.startsWith (CCSSValue.PREFIX_RGB) &&
             RegExHelper.stringMatchesPattern (PATTERN_RGB, sRealValue);
    }
docs: Check if the passed String is valid CSS RGB color value. Example value:
  <code>rgb(255,0,0)</code>
  
  @param sValue
  The value to check. May be <code>null</code>.
  @return <code>true</code> if it is a CSS RGB color value,
  <code>false</code> if not