Power themes are like enhancements and power synergies, but they don’t add new abilities to your power suite. Instead, they color how your power presents itself. You might add an elemental effect to your power, or make it based on technology rather than on the superpower gene.
Because the actual effects of power themes are limited, you may purchase one for free. Each theme beyond the first added to a power costs one stunt. Like power synergies, each theme has a short list of enhancements, drawbacks, and collateral damage effects, which become available to purchase or select when you purchase the theme.