Returns an <code>RGB</code> corresponding to the given pixel value.
@param pixel the pixel to get the RGB value for
@return the RGB value for the given pixel
@exception IllegalArgumentException <ul>
<li>ERROR_NULL_ARGUMENT - if the argument is null</li>
<li>ERROR_INVALID_ARGUMENT - if the pixel does not exist in the palette</li>
</ul>
Returns an <code>RGB</code> corresponding to the given pixel value.
@param pixel the pixel to get the RGB value for @return the RGB value for the given pixel
@exception IllegalArgumentException <ul> <li>ERROR_NULL_ARGUMENT - if the argument is null</li> <li>ERROR_INVALID_ARGUMENT - if the pixel does not exist in the palette</li> </ul>