Is it possible to completely customize the layout of a card? For example, I might want to use PHP to output different things. If I have a color column in my db I could use that to change the color of the field, etc.
I must disappoint you. It is not possible to do it in a nice way. However you can take a look at components/com_grid/layouts/CardView.php. This is where the output is generated. You can change the code here to suit your needs.
There were some ideas about some kind of card templates. We might implement them some time in the future.
