There are no common standards I've ever seen or read about assigning specific colours to up/download, and when trying to come up with a standard, it would have to depend on the context of the buttons. Even if you went with red=bad and green=good, an uploading application would want to assign the colours to a different direction to a downloading application.
A piece of software I have to use regularly has done this, using red and green buttons to choose between wiping the settings on the device and replacing them with your computer's settings, or wiping the settings on your computer and replacing them with those on the device. Which is which?
What you can do is look at the shape and layout rather than just the colours to differentiate the buttons.
At the moment the only difference between the actions is the bottom 12x12 pixels on a 50x25 pixel button, which is probably why you're looking into how to make the buttons look different. By rearranging the elements, you can make the buttons look much different from each other, and this could be combined with colour to make a bigger difference.