Your forks are discoloring ??? Are you talking about the lower fork legs ??? That's almost natural for aluminum parts.
However, you may wish to try this - Get some S100 cleaner in a spray bottle. Follow the directions as to use. Spray on surfaces to be cleaned, allow to sit for several minutes and hose off. Try to keep any high-pressure water spray from the front axle/wheel bearing area.
S100 will take off nearly any tarnish that will build up on aluminum or steel surfaces. If there is an area that is particularly tough, take one of those yellow and green dish washing sponges and after the S100 is sprayed on and has soaked for a few minutes, scrub the area with the green "pot scrubber" side of the sponge. Job done.
Another thing that appears to work well are the Mr. Clean "white sponges". Again follow the directions - dampen (not soak) the Mr. Clean sponge and wipe the area thoroughly and just about all tarnish will be removed.
You can protect the lower fork legs with a good coat of aluminum polish or car wax.
It is a lot of work, but the outcome is worth it. The actual polishing is the easy part. The sanding is where the work is, and the better the sanding job the better the final product. There are, at least on mine there were, lots if rough machining spots on the forks that take a lot of sanding. Do a search and study up on it, there are plenty of good threads on here about polishing. Once you are done you will find plenty of more parts you can polish.