How does this effect work on Picnik?

so, lately i've seen alot of photos where they have this really cool effect where everything is black and white except for a few random things which remain in color. Whenever i ask about it they say to use Picnik, but i can't seem to find it. Can someone please explain how i can do this?How does this effect work on Picnik?
Click on Create, then Effects, then scroll down and find Black and White.





Click on that and there should be a little box appear saying Effect Painting.





The picture should come fully out on black and white effect and to 'colour splash' (add colour to black and white), click Original in the paint mode and then apply it to the place on the photo where you want the colour :)





Hope this helps.