Sunlight is wide-band (see "black body spectrum"). This is why a white object (that reflects all light equally) and a yellow object (which mostly reflects reds and greens) are discernible under such light, even under sunset light which is visibly yellow or orange. The sunset orange light still contains many other colors.
A yellow object and a white object would be not discernible under a very narrow-band yellow light, or a mix of two narrow-band red and green lights of right proportions. This is how LEDs and lasers emit light, but totally unlike hot objects (like Sun) or fluorescent lamps (like "natural light" LED lamps) emit light.
Look, my point is simple: if you agree that snow and sugar are white, then the sunlight is also white.
It has to be because white was historically described as the color of the snow (or whatever is white) under the sunlight.
Now, if you want to adopt a more precise definition of white and other colors, based on (not so) recent scientific insights about the light, you can. Then the sunlight is not white, neither is snow or sugar. And is also certainly not yellow.
Let's be honest, the sun light is almost perfectly white, and kids use yellow to draw the sun, because it wouldn't make sense to draw it with white.
A yellow object and a white object would be not discernible under a very narrow-band yellow light, or a mix of two narrow-band red and green lights of right proportions. This is how LEDs and lasers emit light, but totally unlike hot objects (like Sun) or fluorescent lamps (like "natural light" LED lamps) emit light.