How to Paint Your Walls in Photoshop
Use the Pen Tool to Make Selections
The simplest way to make selections around walls is with the pen Tool. Select the Pen Tool and click on each corner of the walls. If you need to change a point, hold CTRL/CMD and click and drag the point to the desired location.
Once you have completed the path around the wall, right-click inside the path and go to ‘make-selection’. Feather the radius by .5 px to make a realistic edge.
Change Color with Hue/Saturation
After making a selection around the wall, go to ‘Layers – New Adjustment Layer – Hue/Saturation’. The selection you made with the pen Tool will automatically load as a Layer Mask for the Hue/Saturation Adjustment Layer.
If there is something on the wall you don’t want to Colorize, use the Pen Tool to create a path around it then right-click and make the path into a selection. Once the selection is active, go to ‘Edit – Fill’ and choose black. This will make the Layer Mask black in the selection, hiding the Hue/Saturation Adjustment Layer in that area.