Why is the steamed bread at home not as white as the steamed bread sold outside?

Why steamed buns at home are not as white as those sold outside. There are many reasons for this. First of all, it is related to the quality of flour. Good quality flour will be shredded after fermentation, and steamed bread is of good quality and whiter. The second one is related to technology. Adding soda properly after fermentation will make steamed bread whiter, and if it is added too much, it will turn yellow. The third is related to the temperature of steamed bread. Fourth, unscrupulous merchants may add a proper amount of whitening agent, and steamed bread will be whiter. The above is the reason why my analysis is relatively white.