Typical copper jackets are actually a gilding metal alloy: 95% copper 5% zinc. Technically, this is a brass alloy. We just call it copper jacketed. This covers the vast majority of modern jacketed bullets.
Many gold colored bullets are golden because they contain more zinc in the alloy. One of you would have to call MG to find out their exact zinc content.
Other bullets are golden or nearly white because they are actually a cupronickel alloy: 75% copper, the rest nickel with some manganese and/or iron for additional strength.