If you're talking about removing mold and mildew from brick, yes, you can use a pressure washer on low power. In fact, you could wet an area of the wall you want to clean (working your way from the bottom up) with a hose, brush on a mixture of 1 cup bleach to 1 gallon of water, let sit for a few minutes, and hose off. If you want, you can use a nylon bristle-brush or push broom to do a little scrubbing. Don't start from the top down because you'll cause streaking. As you work your way up the wall, just rinse the area you just cleaned as well as the previously cleaned area below. It would be best to do this in the Fall especially if you have plants. The bleach may kill your plants. There are bio-degradeable cleaners at the Home Centers. (They're all over the WEB too ...)
If you're talking about cleaning brick molding, you can wash it by hand as per above. Brick molding is the 'trim' that goes around the exterior of a doorway. This, of course, is a much smaller job.
Now, back on washing your brick. As per your reference to discoloration, there will be a difference after you wash. However, it's a GOOD kind of difference. The brick will be clean! The key is to clean the ENTIRE wall/facade. If you clean only part of it, well, part of the wall will look clean and the rest won't. So again, in short, wash the entire wall. The clearn, per se, won't 'stain' the brick. Just don't use high pressure on the wall. Yes, you may cause damage to the pointing. Other than that, if you have more ?'s, post up!