Oops, it doesn't look like 'colon day' is a national day..

Other days

bow tie

Bow Tie Day
donate your hair

Donate Your Hair Day
cat girl

Cat Girl Day
lisp

Lisp Day
bounce

Bounce Day
believe

Believe Day
self care

Self Care Day
ruby

Ruby Day
cuddle up

Cuddle Up Day
self appreciation

Self Appreciation Day