Use FindFormat on a Range

You can't, from the UI. It would be like finding all words that aren't "Bob".

You could autofilter and then filter by color.

FindFormat sets the Format option for the Find command. You can set what format to look for, but not what not to look for--that is, you can look for a specific fill color, but you can't look for "anything but clear".

There are ways to do this other than FindFormat. How do you want to use this?