We raise our own grass fed beef and it is delish! The secret is to slaughter them at 18 months before they start to get tough. This way you get tender lean meat with out a lot of inter-muscular fat. "Marbling" is usually achieved by feeding grain and helps with flavor and tenderness in full grown beef.
You find yellow fat in some dairy breeds like Jersey. The yellow color is from the high beta carotine content. I think it tastes great. I have never noticed any metalic taste in ours.
Anyway grass fed is lean and should not be over cooked.
