I have seen this question asked over and over again on numerous online Photoshop (and other digital graphics) forums:
How do you create a black and white image where only part of the photograph is in color??
I’m here to tell you that this is one of the easiest tasks to accomplish in Photoshop and requires almost no Photoshop experience.
Below you’ll find that I’ve developed a simple step-by-step tutorial on how to do it:
1) We start with a colored photographic image of your choosing. You need only to decide what portion of it you want to keep in color. For this picture of my son I’ve decided to keep the tires in color for this demonstration.
2) Now copy the background layer. You can do this by dragging and dropping the first (top) layer onto the ‘create a new layer‘ icon, like what Ive demonstrated below:
3) Now let’s convert the top layer picture to monochrome (also called black and white). There are many ways to do this and probably the most well known way (and preferred way IMO) is to use the “channel mixer”. However, for this tutorial I will choose instead to use the desaturation tool by typing Control+Shift+U.

4) Now let’s add a layer mask to the top layer. This can easily be done by simply clicking the button, like what I’ve pointed to below.
5) Zoom into the area of the photograph you want in color and select the “layer mask” you just created by clicking on the layer mask once it has been added.

6) Now select the Brush tool and choose black as the foreground color. The brush size will depend greatly on the area you will paint. Be sure to set the hardness to 100%. Carefully paint on the layer mask (in black) all the areas you want to reveal. This step make take just a little while depending upon the areas you will be painting over.
7. That pretty much does it unless you choose to sharpen (or otherwise enhance your image in other ways) your photograph just a bit afterwards. The finished product is below.

Easy enough, R.I.G.H.T.?
Now you try and post your before and afters.