So... back in the day we accidentally switched the Electrum and Radium pigments when we made our first batches. Consequently the name doesn't really match the color anymore, but it's been far too long to change them back, so here we are.
When Radium is applied over black it does a slow transition from yellow to gold to green before your eyes.
Note: Radium must be used over a dark basecoat. If used over white or a light color, it appears reddish-orange.