I can confirm that deleting the "Shortcuts" App is one of the culprits of this issue - for me. On my iPhone 12 with iOS 14.5, AFTER I deleted the Shortcuts App, my Storage Category bar became all grey. Then I tested it on my iPad with iPadOS 14.5:
- First verified that the Storage Category bar was OK and colored
- Deleted the Shortcuts App > Stayed colored
- Rebooted > Became all grey!!!
Subsequently tested it in an older spare iPhone on iOS 14.3, same exact result where upon deleting the Shortcuts App and rebooting the device, the bar became all grey.
More detail: When this happens, at the very bottom of iPhone Storage screen, taping on "Other" shows Zero KB for "Other System Data". I believe this is causing it. So in conclusion, somehow deleting the Shortcuts App messes up the "Other System Data" size, causing the Storage Category bar to remain confused and grey.
Edit1: Reinstalling the Shortcuts App does not resolve it. Will post other attempts at resolution ...