Is is normal for roast beef to be green?

Answer 1

From the USDA...

Iridescent Color of Roast Beef:

Sliced cooked beef or lunch meat can have an iridescent color. Meat contains iron, fat, and many other compounds. When light hits a slice of meat, it splits into colors like a rainbow. There are also various pigments in meat compounds which can give it an iridescent or greenish cast when exposed to heat and processing. Iridescent beef isn't spoiled necessarily. Spoiled cooked beef would probably also be slimy or sticky and have an off-odor.

Answer 2

No! Meats can become oxidized and become sort of rainbow colored, and that isn't good. Green colored roast should be thrown out.