Peel the potatoes and cut them into bite-sized pieces. Soak in water for about 5 minutes, then drain.

Place the potatoes in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for about 6 minutes. Drain the water, then mash the potatoes while still warm with butter and salt.

Add milk to the mashed potatoes and mix well. Divide the mixture into three equal portions.

In a plastic bag, combine one-third of the mashed potatoes with sakura denbu to create pink mashed potatoes.

In another plastic bag, combine another third of the mashed potatoes with aonori to create green mashed potatoes.