White balance (WB) is a critical back-end processing function in image sensor to keep color constancy under various lighting conditions by adjusting RGB intensity. In this work, we proposed a novel gate-controlled gain tuning method for FDSOI one-transistor (1T) pixel to achieve WB inside sensor. Based on the structure of photoelectrons coupling transistor back-gate, the 1T pixel output gain is modulated by front-gate according to transistor transfer characteristic. About 5x photoresponse modulation range in RGB spectrums (nonlinearity<3%) was experimentally demonstrated by 22nm FDSOI-based technology, which enables in-sensor WB with almost equivalent performance (Delta-E deviation<0.1) achieved by using traditional back-end WB.