Well technically your sink isn't pink - the color is copper. It is the color of copper before it has been oxidized. Think of the difference between a new penny and one that has circulated for awhile and turned brownish.

What will happen will depend on what your sink originally looked like.

Copper sinks either have what are called living finishes which means there is no artificial "patina" which is done at the factory and so the copper changes and blotches as various elements hit it. It will turn bright coppery where acidic substances hit it like lemons or ketchup and then become dull again as they patina. They will never turn dark brown and they wll never look uniform. You either love a living finish the way people love old jeans and real rumpled linen or you hate it because it is never going to be shiny.

You could theoretially polish a copper sink to get it shiny the way you might shine up a copper pot that is being displayed but no one in their right mind would want that kind of upkeep for a sink. Also shiny copper objects that are displayed often have some kind of lacquer finish treatment that keeps them from oxidizing but they aren't meant to be used as they can't withstand the kind of abrasive cleaning that a sink would normally get.

If you bought your sink and it was dark brown when you bought it, you had a an artificial patina that was done at the factory and you scrubbed it off. It is NEVER going to look like that again because copper doesn't aquire a patina that looks like that. Those finishes are artificial looking.

I have a kitchen sink with a living finish which I love. I am posting a picture of the sinkn bottom which shows the variegations of the sink. The only think I do to clean it is to use a soft sponge with Dawn if there has been something greasy in it. But otherwise less is more especially since natural copper has anti-bacterial properties.

People sometimes have fun with their living finishes as there are pictures of people who have used ketchup to write out Happy Birthday because when the ketchup rinses off, the letters will be shiny copper until they oxidate again/

I have a sink in my guest bath which does have the artificial dark brown factory "patina". That was fine with me because it wasn't going to get any kind of hard use and so it would never be scrubbed with anything at all that would take off the patina. I wouldn't want to have a living finish in the sink of my powder room though because I was going for a different feel so I knew what I was getting into and it was a deliberate choice.

Here is a picture of my kitchen sink with a living finish. This is approximately what your sink will look like as it acquires a "patina" but it will never be the dark brown of the original finish.