Selective Black and White.

First you have to make a copy of the original image on its own layer.

This gives you 2 layers with exactly the same image on.

The top layer is changed in to black and white by using the channel mixer tool. 

To get the colour to come through the black and white layer the eraser tool has to be used, so it is selected.

From there the size of the brush and hardness of the edges can be changed so as to get the best result off the image. 

In this image the design on the back of the jacket has been erased off the top layer so as the colour layer can be seen through the layer.