Spend the indicated type of credits to unlock the corresponding bonus song:

Battle Theme (GF): 2 Blue credits, 1 Gold credit, 4 Red credits
Battle Theme (Metroid): 2 Blue credits, 1 Gold credit, 4 Red credits
Gandrayda: 2 Blue credits, 1 Gold credit, 4 Red credits
Gryyo: 2 Blue credits, 1 Gold credit, 4 Red credits
Gryyo (Thorn Jungle): 2 Blue credits, 1 Gold credit, 4 Red credits
Helios: 2 Blue credits, 1 Gold credit, 4 Red credits
In the Cockpit: 2 Blue credits, 1 Gold credit, 4 Red credits
Omega Ridley: 2 Blue credits, 1 Gold credit, 4 Red credits
Phaaze: 2 Blue credits, 1 Gold credit, 4 Red credits
Pirate Homeworld: 2 Blue credits, 1 Gold credit, 4 Red credits
Skytown: 2 Blue credits, 1 Gold credit, 4 Red credits
Steamlord: 2 Blue credits, 1 Gold credit, 4 Red credits
The Corruption: 2 Blue credits, 1 Gold credit, 4 Red credits
Title Screen: 2 Blue credits, 1 Gold credit, 4 Red credits
Valhalla: 2 Blue credits, 1 Gold credit, 4 Red credits