I've had a few names used for an orange car I had.
Agent Orange like Shaggimo said.
Orange Crush, my younger cousin called it that because it reminded her of the pop.
Project Orange is what I called it when I was working on it.
Some other decent one's I've heard are
Juice[d] for an orange drag Chevelle
No Pulp for a V6 orange Mustang, because it made under 200HP.
Clockwork Orange for a friend of mine's orange Porsche, based off two parts. One A Clockwork Orange is one of his favourite books, and two he said 'like clockwork' something always goes wrong with it.
My dad had a Cutlass that everyone called "the Orange Peel" although I have no idea why.. it wasn't even orange haha.. and it didn't refer to the orange peel effect on paint.
Vitamin C
Sunspot