You are allowed to drink a whole lot of things up until 4 hours before the colonoscopy, as long as they are classified as "clear liquid" beverages. Even coffee is okay. That's universally agreed upon. Once the 4-hour mark hits, you can't eat or drink anything.
I'm asking about the prep portion -- where you put the Miralax into Gatorade, and drink it. The only question is whether light blue Gatorade is allowed. I think it is, but I'm finding contradictory info online.