Correct on changing the bulb. The ring itself only bends/refracts the light from the bulb. The color output is limited to the color bulb that replaces the OEM part.
The dull yellow color is a thing of the past for me. We are seeing so much more xenon/brilliant white on the headlamps as a design standard. Take Aston Martin V8 Vantage
forexample with its LED headlamps.