What you want to do is called selective coloring or splash coloring with gimp.Gimp is a free photo editing software you can get it here if you don`t have it and you want it http://www.gimp.org There are two way`s you can do this The first way is to Put your picture into gimp and then duplicate it by left clicking on the icon that looks like a picture inside another picture next to the one that look`s like a anchor in your layers,chanel box. Make the layer you have just made is highlighted by left clicking on it. Then Desaturate the layer that you have just made and make it B&W by left clicking on colors and drop down box click on Desaturate. Apply a layer mask to the layer by right clicking on the layer and in the drop down box left click on Add layer mask... make sure that White (full opacity) is selected click on the add Button at the bottom of the drop down box make sure that you are you are on the layer mask box, not on the image itself by clicking on the layer mask box next to the layer you made. Then use the black brush to paint on the layer mask That will bring the color back to those areas. If you make a mistake, change the brush to white and go over it.
The Second way to do what is called selective coloring or splash coloring with gimp.Here`s is how you can have some part`s of a picture B&W with some part`s color. To make that kind of picture with Gimp. First open gimp put in the picture that you want to make with some color and B&W. Use the path tool to in-close the part of the picture that you want to be color. The path tool will leave a lot of little dot`s around the part that you want to be color. After you in close the part that you want to be color go to your keyboard and push the Ctrl button to close the path then go to select click on it a drop down box will come up click on from path then go back to select and click on it again in the drop down box click on invert. Then go to color`s click on it and in the drop down box click on Desaturate if you want all the picture to be B&W and just have that one part color. Or if you want to have some color in the B&W part and full color in the part you select then click on select and Hue-saturation and in the Hue-saturation box use the
slider button where it say`s saturation to adjust the amount of color that you want in the B&W part then click on ok at the bottom of the box.If you want two or more part`s to be in color than click on the dot`s that path tool make`s and use the path tool to in-close the other`s part`s that you want to make color but don`t click on the first dot or the last dot that the path tool make`s or it won`t work click on one of the dot`s in-between the first and last dot`s that the path tool make`s. Do this for each path that you make.Here are some tutorial`s that can also help you with that.
http://www.youtube.com/watch?v=uUHZxXvgAK8
http://www.youtube.com/watch?v=c282wZpmbI8
http://www.youtube.com/watch?v=JtAFDPiIvOY
http://www.youtube.com/watch?v=K6jgHrLkpuQ&feature=related
I hope this can help you.