A paintball vest I got was made of those foam like material (very similar to a mouse pad or knee/elbow pads). That stuff just kept on soaking up acrylic paint, so I eventually just spray painted and the color did stick. However, trying to do anything more than one solid color would be very time consuming.
As for leather armor, here's a pic of Gambit I did where I just gave it a nice coat of regular spray paint and it turned out really well. You may get more shine than you'd like for Robin, so you may have to find a different kind of finish.