Mao's semblance is being able to fire shockwaves from his punches (hadouken-esque). The shockwaves have a range of 30 feet and can be charged for additional damage. Mao can channel his semblance into his fist to instead give his punches additional damage instead of having to fire the shockwaves for damage.
The stamina exerted to use his semblance is proportional to how much stamina he would use performing a punch of equivalent force. Additionally, past a certain point, the recoil of the shockwaves also start to wear him down at an increasing rate proportional to the difference between the shockwave's strength and the threshold.
The shockwaves are the color of his aura, and the stronger the shockwave, the stronger the color. The same concept applies to when Mao channels the semblance into his fist.