First, are you sure its a RO and DI, cuz it only has 3 stages, maybe I'm confused though? Do you have a link to where you got it from?
Are the cords already hooked up for you? There should be an inlet that you hook up to your water source. Then one for waste water and one for good water. My guess is blue outlet is your good one. But not sure. Can you tell by the way the cords are hooked up? The inlet shoudl go to the sediment filter, then to the carbon filter, then the membrane last (that hard tube on the top), the waste water tube is what is rejected from the membrane, and the good water is what comes out of the end.
Maybe that idea will help you determine which one it is? Good luck. Post some more details and I may be able to find the answers online.