SoulOfTheMedley  Here is the list of roles for characters.

Red: Open
Yellow: Temporary role - Not open
Blue - F: Open
Green - M: Open
Gold: Open
Silver: Open
Crystal: Open
Ruby: Open
Sapphire: Not open
Emerald: Open for temporary role
Diamond: Open
Pearl: Open
Platinum: Not open
Black: Open
White: Open
Blake: Open for temporary role
Whitley: Open
X: Temporary role - Not open
Y: Definitely not open
Sun: Open
Moon: Open
Sword: Open
Shield: Open

Any of the rivals, including the game protagonists if they are included in the game as a rival (for example, Brendan) are open if we include them. However, I might deny you the role because my OC might be shipped with some of them.