Dead coralline turns white.
Coralline comes in many different corlors..different shades of purple, red, green, orange..
Whichever color you would like to end up with the most of ...do this...scrape some of the coralline you like with something sharp (a knife, scissors..) and allow it to float around in the tank..it will seed other areas with that color coralline. Maintain good flow, good lighting and your Calcium level (and good parameters in general) and your coralline should take hold. Be patient, it doesn't grow crazy fast, but it will grow if you do these things.