Pixiv user tags: "※The milk is diluted in the print (doujinshi) version" and " Yuanyang "
Also relevant: Porurin also held a niconico live broadcast to take fan submissions for more yuri-themed senryuu that "Midori would enjoy", for inclusion in Vol.4 of the comic.
Updated
*flap*Midori-chan's "tea stalk"... is some kind of yuri sensor...?Aah~ shoo good! The tea stalks are all going ping!*flap*In the language of flowers, the white lily signifies purity and innocence. Wonderful, isn't it?
wikipedia*whirl**whirl*the lily flowerslily = yurian immaculate pure whiteBlooming in the milk