Here are a few suggestions based on parent reports:
Reducing the dosage to the smallest recommended dose and give more times throughout the day. (less product in the water or juice has less of a taste and gives the tastebuds time to adapt)
Use fillable vegetarian capsules and add the powder to them and have your child swallow the pill form.
Use a child's medicine dropper or syringe and squirt in the back of the mouth like you would when giving a baby medicine
Use a thermos or other drink container that does not allow the color of the liquid to be seen.
Make into a popsicle by adding the supplement to water or juice and freezing in a popsicle mold.
Hide in a fruit puree or soft serve food.
Hiding in Orange Juice is the most popular reported mask of taste and color