If the Sun put out yellow light instead of white light, rainbows and the spectrum through a prism would not contain all the other colors. Low pressure sodium vapor lamps (the orange-yellow street lights) have mostly yellow/orange output and just a few other spectral emission lines. Ever notice how badly those sodium vapor lights render color? They really suck at it. Try it out for yourself by putting a rainbow or multicolored object under sodium vapor light and observe which colors turn black or gray looking. You will be surprised. The Sun is not and never was yellow.