Mr. j. I would highly recommend vacuum gauges be installed on the filters if you don't have them already. A vacuum reading will be a much better indicator of filter condition than residue in the bottom of the filter.
, as Mr. k notes, indicate that the filter is doing it's job but it may not be at the end of it's useful life. The filter removes "dirt" via vacuum from the fuel lift pump while the engine is running. When the engine stops, some of that trapped "dirt" falls to the bottom and can be seen as you posted.
For example: https://discountracor.com/shop/vacuu...or-rk11-1676e/
The model with the moveable indicating needle will show you maximum vacuum after the engine is stopped.
Edit: Might I ask how long ago was the last filter change done?