You have quite a few choices. You could use any type of metal color from the various paint producers. You could use specialized metalic paints such as MM Metalizers, Alcad, or SnJ. You could use foils such as BMF or others. You could use metalic paint for real aircraft and cars. You could even plate it depending on what color you want.
I like to use MM Metalizers for exhaust and SnJ for finishes. SnJ is very expensive, but by far gives the best results.
MM Metalizers should be applied mask and must be sealed using Metalizer Sealer. Metalizers don't mask well unlike Alcad and SnJ. Paint the model as you want. Paint the metalic elements. Give the model a gloss clear coat. Apply the decals before or after weathering. Give it another gloss coat to ensure decals won't show and come off and to keep the weathering from smearing and coming off. Then apply more gloss coats or flat coats. Make sure to wet sand with a very fine sandpaper if you want it to be super glossy. I like to also polish between coats using either Tamiya or Novus polish. I personally don't like Future because it can be distorted and ruin by many things such as MicroSet and water sitting on it. I've never had luck with it.