Zophah on page 141
The correct answer is calcium.

Otto on page 141
But why is calcium white?

Yochanan on page 141
Because it reflects all the colors

Guesticus on page 141
"I don't know" is a very valid answer (it's the name of their national animal afterall :P)

Opus the Poet on page 141
Milk is white because it is a colloidial suspension of fat globules in water that scatters light at all wavelengths equally. The sky is blue because its molecules scatter mostly blue light.

Deof Movestofca on page 141
So purple cows would give grape-flavored milk?