Projet Files Activity Heat Indicator

I have a short attention span and a lot of files in the open / project file view.  It would be great if the files I have recently been active in would be indicated either by color, or highlight.  Even if they are saved, even if I just peeked into them.  Perhaps another iteration can bring actual heat - like if I have been in and out of two files all day long, those are easily differentiated from the ones I looked at once.