I googled it.
A very clever man who knows all about navel fluff speaks up.
But Why is It Always Blue?
It has been observed that belly-button fluff tends to be of a blueish tint.
Sometimes it looks a little grey, sometimes purple, but generally it's a pale blue
Most clothing has elements of blue or white. The dyes in black clothing,
for example, are often not actually black but a very dark blue.
And the next time you see a picture of Kasparov you can think to yourself.
"The fluff in his belly button is blue just like mine."