Can pearl powder be whitened when put into shower gel?
Sure, but it's best to whiten it in body lotion. It will be washed off when used in shower gel, but the effect is definitely better than that of ordinary whitening shower gel.
Another way is to mix some milk with pearl powder after bathing, rub it on your body, massage and absorb it, and then rinse it off. This is also good, just like making a mask.