There are cleaners you can use to wipe that off, too.
Safely removes accumulated brake dust, oil, dirt, stains and light corrosion from premium quality wheels without damaging the delicate surface. Brake Buster is a unique cleaning gel that adheres to the wheel surface and penetrates the dirt deposits to clean them away. Brake Buster deposits a...
psdetailproducts.com
TUGA Devil Special® is an acid-free, phosphate free, highly efficient wheel cleaner which easily removes baked on brake dust and a variety of heavy contaminants.
www.carpro-us.com
CarPro Iron X (500ml) is a highly effective, acid-free and pH balanced decontamination product safe for use on most automotive surfaces!
www.carpro-us.com
Adam's Wheel Cleaner is the best wheel cleaner you will ever use; it cleans wheels while dissolving brake dust. The color changing formula of Adam's Wheel Cleaner lets you know its working. Plus, it doesn't smell as bad as some other wheel cleaner out there!
adamspolishes.com
Those are for wheels. Most are also safe for paint, in case there is brake dust or contaminants in your paint, but read the instructions.
Then there are the *real* brake cleaners:
https://www.crcindustries.com/brakleen-174-pro-series-brake-parts-cleaner-non-flammable-29-wt-oz/ (this one causes cancer and Parkinson’s, for real, but is by far the best one. wear gloves and VOC mask and eye protection if you use it, and use it sparingly; you also cannot buy this in CA)
https://www.crcindustries.com/brakleen-174-brake-parts-cleaner-scaqmd-1171-compliant-14-wt-oz/ (this is the non-chlorinated much safer version; doesn’t work quite as well but also doesn’t kill you, so YMMV)