HOK gold base coats come in three colors:
BC-01 Solar gold/medium gold on the yellow side
BC-07 Gamma gold/darker gold on the copper side
BC-12 Zenith gold/light gold on the silver side
In the color book they all look very close to me.
It's up to you what color base but I'd go with solar gold BC-01.
The metallic bases also come in finer metallic or
FBC= fine base coat.