I used to think that period blood was going to be blue because in the commercials in which they do an absorbency test comparing two different brands of sanitary napkins they use water with blue dye in it.
A childhood belief about periods

others believed things like this
- I was horrified when my first period arrived. It wasn't blue, like in the commercials for sanitary towels.— Jane
- I used to believe that menstruation fluid was blue because of the way TV commercials showed it. — matias
- Eifel 65 - Blue
I'm Blue (if I was green I would die...)
[I'm blue, da ba dee, da ba di.]— Matt - I used to think that blood was blue until it touched air.— paetrw
- I thought the blue veins in some cheeses were actually blood vessesls!— Helen
- I used to believe that sanitary napkins was the name of moist towellettesAnon