What happens when there are no more mana tokens of a color in the supply?
There's no component limit on mana tokens.

Use some other indicator (dice or other objects) to track your mana tokens for the turn, if needed.

The game comes with enough tokens for players to store their maximum allowance of mana crystals (page 6 of the rules). However, there's no mention of limits for mana tokens. The game explicitly tells you to gain mana tokens when you've hit your limit of crystals, so it seems unlikely that you wouldn't be allowed to do this just because other players are also holding onto crystals.

Also, based on the mana crystal limit, we expect that the rules writer will make limitations explicit.

While it isn't covered explicitly in the rules, other players have said the same:


  There is no limit to the number of mana tokens you may have, but they go away at the end of the turn whether used or not.