Hi, and welcome!

There are certainly differences in the equipment level of the two bikes, but I don't think any would appreciably impact your enjoyment of the bike. Save possibly for the 2x10 drivetrain vs. the 3x9 like CT_Sean said above. I, too, would prefer the the 3x9 drivetrain on the DS3 personally. I would recommend not discounting your preference on color, either. You're going to see the color every time you ride the bike and, if you really like the blue, you may end up thinking about that blue every time you ride your black DS4.