Magnesium is showing as red on my heavy metals, is this not a mineral?

Magnesium is also a mineral, yes. As stated at the bottom of your heavy metals results page: "Please note these heavy metals are not to be confused with minerals." 

The magnesium listed in your heavy metals section only, is the derivative of magnesium known as Magnesium Oxide, which is commonly found in, antacids, medications, bath care products, skincare products, hair care products, is also used as an ingredient to absorb or soak up liquids, and as an opacifying agent in skin make-up for hiding blemishes