Ok around here metal roofs are done with a similar panel to what they build barns with. All of that has a baked on enamel coating that is guaranteed no fade for 20-30years depending on color. If you do go with one make sure you get 26ga metal as it holds up better and is less likely to be hail damaged. Make sure whoever you get to do it knows what they are doing and does not provide for a space for water to get trapped in between the metal and the roof decking....
Mueller, Inc. - Residential Metal Roofing
There is a very good site to look at.