What colour ends with an a that has seven letters?

A seven letter color that ends with A is:

• fuchsia (pink)
• magenta
• regalia (purple)
• sangria

Sangria is a beverage made in Spain. It's color depends entirely on the ingredients used. Since different recipes call for different ingredients a particular color can not be attributed to Sangria.

Nobody who has seen a Radioactive Hazard sign would ever call Magenta "Red">