This sounds complicated but keep at it. I use this technique all the time. Once you've mastered it, you can create all kinds of exciting color effects.
Instructions: Using Adjustment Layers to Change Colors in a Room (etc.)
Open photo in Photoshop. At the bottom of the Layers palette, you’ll see a row of icons. Click on the one that looks like a circle, with one half light and one half dark. This is the Adjustment Layer icon, and from here you can add any type of adjustment layer. An Adjustment layer is like a filtering layer. It affects the pixels below it, but in a non-permanent, adjustable way. Add a Hue/Saturation adjustment layer, and in it’s dialogue box, check the colorize option. This will give you a monotone image, the colour of which you can control with it’s Hue, Saturation and Lightness sliders. The Hue slider controls the colour of the image. The Saturation slider controls how intense the colour is (left makes the colour greyish and muted, while right makes it very intense and vibrant). The Lightness slider controls how light or dark the colour is.
Once you’ve checked the colorize box and you’re seeing the image in monotone, keep an eye on the wall colour and play with the sliders until you see a colour you like. Now, this is going to affect the whole image. To limit the colour to only the wall go to the next step.
When you’re happy with the colour, click OK,and you’ll see the adjustment layer appear above the image layer in the Layers palette. A white rectangle has appeared next to the adjustment layer’s icon. That’s a layer mask, and it’s purpose is to mask, or hide the effect of the adjustment layer. It’s important to remember that with any layer mask, black hides and white reveals, meaning that if the layer mask is filled with black, it will hide the effect of the adjustment layer, and if it’s filled with white (as it is now), it will reveal the effect. Make sure that the layer mask is selected by clicking on it’s icon in the Layers palette. Now, anywhere on your image that you don’t want the coloured effect to show, you can hide it’s effect by painting with a brush loaded with black paint. Give it a try. Choose a paintbrush, make sure you have black paint selected and start painting on any part of your image that you don’t want colourized. You’ll see the colour effect disappear, and the original colour of the image reappear. Now, all you have to do is paint over any part of the image that you don’t want coloured.
The great thing about Adjustment layers is that you can change them at any time. If you want to try some different colours, double click on the adjustment layer’s icon and the original dialogue box will appear, complete with the settings you originally used to create the current colour. Use the sliders to create the colour you want on the walls. You can use this same technique to try several colours on anything.