The first thing you should do with any image is clean it up. Dust, scratches, and uneven tones all need to go before you start working on it. Use the clone brush to get rid of defects, and in some cases the healing brush can be used to add texture to blown out areas. The uneven tones will be taken care of in the levels. It's not required to do any of this, but it will definitely help out your final product. If you're not experienced with levels, this might be slightly confusing, but once you know your way around, this step only takes a couple seconds.With a colorization, levels are extremely important. Levels can be found under Image -> Adjustments -> Levels.The levels of my original photograph looked like this:See those low areas to the right and the left of the "mountain"? By bringing in the little arrows on the right and left (which represent light and dark values) towards the main mass, you will acheive a much better distributuion of values. It should look like this before you click ok:Before and after levels: You can also just use auto levels, but that won't always give you the results you desire. By tweaking the levels by hand you can select just how you want your image to end up. You don't have to put the markers exactly where I did, just play around with them until it looks right to you. The middle arrow is the mid tones, which can be adjusted as well.After you've done all this, go up to image -> mode -> CMYK color. THIS IS IMPORTANT. It won't work if you don't do this, so don't forget.