"Blue-black metallic" is it's proper UK Name.
Big Bumper GTis came in 3 types of Blue - "Bright blue metallic" (C3), "Royal blue metallic" (Y6) and "Blue-black metallic" (9982).
Now the interesting bit...
"Blue-black metallic" was a 16v only colour, it wasn't even available as a factory option for the 8v. So, if your car is a 8v it is VERY rare indeed!