Written instructions (Firestorm viewer):
Right click the wall, and choose Edit.
In the edit window, check the “select face” button.
Click on the wall you want to tint.
In the edit window, click on the Texture tab.
Click the Tint color box. Pick your color, and hit ok.
If you want to save that color for other walls, you can save it by dragging the color onto one of the little color swatch boxes in the color picker window. Next time you need it, just click on that color swatch.