How do HK restaurants keep wok-fried scallops white, with no visible sear marks?
Your scallops are (beautifully) seared on the outside because they are cooked all the way through in a very hot pan. The scallops in the Chinese stir fries stay pale because most of their cooking is done at low heat.

They are likely cooked twice: first they are velveted (meaning marinated and oil-blanched) and then very quickly stir fried to reheat. In more detail, we have three steps:


marinate in a mixture of cornstarch, wine, and egg whites
blanch in oil at a very low temperature (at most 300F/150°C)
make the rest of the stir fry over high heat, and add the meat at the very end of cooking


Unfortunately, velveting is an involved project. It involves an oil-blanch which leaves you with a lot of waste oil. For home cooking, some recipes suggest to replace the oil-blanch with a water blanch.