Exploration Energy (Yellow):
You will gain 1 Exploration Energy every 10 minutes, up to the maximum capacity that you can currently hold at your progression level (Maximum 70 at player level 50).

Clan Energy (Purple):
You will gain 1 Clan Energy every 4 hours, until the maximum of 3 Clan Energy is reached.

Arena Energy (Red):
You will gain 1 Arena Energy every 1 hour, until the maximum of 6 Arena Energy is reached.

Once the maximum threshold is reached, you will not accumulate any more Energy until the Energy is used.
However, Energy that you buy will be added on top of your maximum. As soon as you go below the maximum Energy capacity, you will start accumulating Energy again.