Set Google Maps to satellite mode, or download Google Earth. That should get you 90% of the way to where you want to go. Or, you could take a look for scientific satellite imagery. You have to jump through a few hoops and really know exactly what you want, but you can get some really nice data that way. I got heightfield imagery of the Nazca plateau in Peru from down to a resolution of 30m per pixel, which is pretty good for South American imagery. That came from a Japanese satellite called ASTER.
As regards rivers, you're right—they do usually appear brown or green thanks to the vegetation that grows along their banks and the silt they are usually carrying. Even up close, you don't often see a river that reflects the sky well enough to really be blue. But in terms of a map, the expectation is that blue = water, so even though that's not really what it looks like, people color their rivers blue anyway. I tried to get away with a green-brown river on a map, and everyone who offered an opinion said it looked wrong.