Ithirahad
Arana'Aethi
Having looked at the code, black-hole colouration is simply a parameter that is randomly assigned to every single system (if memory serves, this is including void systems!) when galaxies generate. Whichever type of stellar object gets placed inside, it inherits the system colour. In this case of stars, this means the visual effect for the star changes color. For black holes, this probably has zero effect except changing the appearance of the icon on the map.