There are a few different ways you can handle color changes in Photoshop depending on what look you are going after. One of the easiest is by clicking on New Fill or Adjustment Layer (the half-black and half-white circle) on the Layer palette. From there choose Hue\Saturation and from the new window that pops up, click on Colorize before changing the settings. Checking the Colorize button will allow an even shift of all the hues in the image to whatever new color that you have chosen. Depending on your image, you might need to change the colors without using Colorize selected so play with it first and see which one gives you the best results.
Another way you can do that is by making a new layer on top of all your layers and filling that layer with the color you want the others to be blending with. Make sure you Ctrl-Click the layer underneath so you get the selection of the image before filling in the color with Alt-Backspace. Once you have your color on that new layer, choose either Hue or Color blending modes from the bottom of the layer blending dropbox (it is to the left of the opacity settings in the layer palette).
Both of those techniques give good results but you can to play around until you find the one that you like best or that works best for the current image you are working on.
Hope that was some help to you Arch0wl or anyone else out there that was wondering how the change colors with Photoshop. I have been using Photoshop since version 3.0 came out, which was about ten years ago, so I should know a thing or to about that program.

I used to make Photoshop tutorials for different techniques, but I have been busy as a late to make any new ones. If anybody else has any Photoshop questions, make a forum post, forum PM me, send me either some email, or IM me and I will do my best to help you out. I will most likely post the answers to your question on the Graphic Design forum so others can benefit from the advice.
Until next time,