OK, this tutorial will explain what i did to color my recent project, "Lumber Mill" which can be seen here at
http://www.deviantart.com/deviation/13377593/. With that said lets get started!

Step 1
First get an image you would like to color or desaturate an image, This tutorial is more for old photos or drawings that havn't been colored yet, for renders try tweaks tut here http://www.visualdesigncore.com/tutorials/photoshop/23/ but feel free to experiment with other works (remember that if it is in color you need to desaturate it)!

Step 2
Now heres how we will set up the image, your original image will ALWAYS be at the bottom and you must NEVER color on it, instead we will use new layers. Its best to make a new layer for different features on the image; for example, in lumber mill I made a new layer for the trees and colored only the trees on the image on that layer, the same for logs the buildings, ect. ( By the way, I will refer to the original image as the BASE layer from now on.)

Step 3
Now take out your magic wand tool (the W key) and select a large area of whatever you are coloring on the BASE layer (Note that it helps sometimes to mess with the TOLERENCE of the magic wand tool, you can change it at the top of the screen, use large numbers for larger areas and smaller numbers for the smaller spots.) Now that you have an area selected on the BASE layer, select the layer for the feature you selected; Example, if you selected some trees on the BASE layer, select your trees layer and color on that with the paint bucket (g key) based on how light or dark it is for best results. Lets say if you selected part of the trees that are lighter then the rest you would use a light green, darker areas of trees would use a darker green.

Step 4
You may notice that the colors dont look good, just set the layer modes for your color layers to soft light, hard light or overlay and see how it looks, i found soft light to work the best but feel free to experiment!

Step 5
Continue doing step 3 until most of your image is colored, you may see some spots wernt colored, just select the right layer and color it with the basic color the layer is made of (for example, if you had trees that were not fully colored, just go over the uncolored spots with a medium green, not too dark or light) after you see that you've gotten most of it hide the BASE layer and look for parts you missed that are transparent, then unhide the BASE layer and color thouse spots.

Step 6
With a lot of work you should have a very nice colored image , feel free to post your results and comments!

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