We have a Blanco Silgranite sink, the colour is anthracite - 11 years old.
We live in a very hard water area.
For the first few years it looked great, now it has faint grey areas / limescale staining. I have spent hours trying to clean it - I have even used the cleaning product that Blanco produce, with limited / varying results.
Once cleaned and then coated with a layer of chopping board oil (the stuff Ikea sell) it looks as good as new for a couple of weeks, then it needs doing again.
I am swaying towards a stainless steel sink when we have our new kitchen, but every Kitchen showroom we have recently visited all favour the composite sinks.