This is for Photoshop
This tutorial will show you how to make certain parts of people black and white while the other parts are still colored, like a sin city effect.
Find a suitable photo that has many colors in it, i choose this one.
Make a new layer above the current layer of the picture you have.
Grab the paint brush and find a decent size that isnt to big, or to small, for this picture i chose a size 20 px brush. Now make sure the color of the brush is black and slowy start to brush over the skin of the person. (or other parts of the picture if you desire)
Once your done brushing over all the parts it should look roughly like this.
Making sure your still on layer two, change the effect to "color"
Here is your finished product.
Note: if you have any spots that didnt get colored in, you can just brush over then to change it to the color you want.
This is my first tutorial, i hope you liked it.