unfortunately i don't know much about iPhones, as I am an android person. their camera reputation is good, tho. do you know if it has a "pro mode"? if it does, white balance should be one of the adjustable things in that mode. If it has pro mode, I'd find out how to turn thai on, and then fiddle with the settings under different kinds of lighting. you'll likely get the best results in natural light, indirect sunlight. but if you want to take pictures at night, there should be a way to either change the warm/cool balance (if it's adding yellows, to tone that down), or directly adjust the WB.