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