Soooo,... I was cleaning my sink today and I punched my knuckle through the bowl,... honest!...
It's one of those Plasticy pre-fab Home Depot kinda' units with the bowl and counter all in one... about 3 years old.... Musta' been a bubble, weak spot in the pour...
Anyway,...
What do you think I should patch it with?...
Does JB Weld come in eggshell white?... ...

Any ideas?... it's a pretty tiny hole... ...

If you can get to that from behind, then maybe Mick has it spot on. A litl sanding & some fiberglass epoxy on it, a bit O glass & more juice,, 2 o 3 layers O that, & let it set up. Surely F/glass epoxy wouldnt attack a plastic?? Try it in a small spot? Anyway, once you solve the "knuckle Dragging" problem, you can get a bit of paint in there..

I was hunting a fix for you & found this. Hey, Ive seen this , but just accepted it.. ahhh, science,,

http://www.wired.com/wiredscience/2010/10/kitchen-sink-white-hole/



Oh, & BTW, youre gonna be able to make a patch hold a lot better if you can find a way to get something to fill that gap & if you can "wet" the surface behind that hole some. Epoxies, hard as they are, are still stronger when theyre  bonding things together, so, maybe you can find a good, strong epoxy & blend some plastic powder into it, or just accept an off color spot, which is probably what Id do.


How thick is the sink wall there? It looks like its about as thick as paint,,

How high up the basin is it?

There's this "plastic weld" stuff, a 2-part epoxy, that comes in about the same yellowish off-white as your sink.. there may be some at Autozone.  

The hole can be backed up with aluminum foil, then fill, sand, cuss, replace sink.  That's what I'd do.  

This a bathroom sink?  Whereabouts on the sink is the damage?  How much trouble is it gonna cause?  I'd stuff something in the hole, then a piece of that wallpaper joint mesh for something to grab onto, and cover it with some good waterproof caulk (which can be found in many colors), smooth it out real nice a perty, and be done with it until I was ready to replace the whole sink/unit.  

And don't clean it so hard next time...  

If the hole is over the overflow drain channel cast into the sink, it won't matter if your repair leaks. If it was me I would tap GENTLY around the whole sink with a small ball peen hammer to see if there are other weak areas before I would bother to repair.
If you are really set on keeping the "marble" top you can cut this stuff with a jigsaw and a fine toothed blade. Buy a cheap metal sink, tape the template to the top, and cut it out, then install the new sink.
You will never be able to make an invisible repair, but if that doesn't matter to you then I would bevel the edge and use epoxy putty, sand it smooth, paint it with lacquer, and the "glaze" it with clear epoxy. You will still see it, and it will bug the h#ll out of you, because you will know where it is.

I'll be darned... JB Weld does come in white...
I think I'll try it... available at auto parts stores for some bizarre reason...
I think it's what Boule'tard was referring too..

I used to use a epoxy called Marine Tex, the stuff was hard as a rock, water proof and came in off white. Don't know if they make it any more. To fill that hole try packing it with a little paper, put some epoxy in the hole to act as a backing then do a second layer to finish and smooth the patch.