Each glyph is oversampled horizontally by a factor of six and then one pixel wide box filters aligned with the subpixel elements are used to generate the component coverage values. The Render extension has been modified to allow ARGB images as mask values which operate independently.
The sub-pixel sampled image clearly shows that additional hinting will be required to avoid color errors along vertical edges of the glyphs. This can be done separately from the changes required within the extension. Look more closely at the diagonal and curved elements of the glyphs; they show the most improvement and least objectionable color artifacts.
The improvement will only be evident when displayed on a digital LCD monitor; most analog LCD monitors aren't pixel sync'ed correctly. The RGB image depends on an RGB ordering of the subpixels on the device; some LCD monitors are BGR.