DIY colored dry rock

[Fishingking3452]

Carib sea makes their life rock which is just dry rock coated in something purple and supposedly has dormant bacteria on it. Does anyone know how to color dry rock like that without haring fish or coral?

 

[Bo.]

Time. Enough time and your white rock will turn nice and purple. This is one year

 

[Fishingking3452]

I know that it would grow coralline algae after enough time but I'm trying to avoid the algae that seems to grow on white rocks.