Oops, it doesn't look like 'no discernable color difference between ground and sky day' is a national day..

Other days

Frozen Yogurt Day

Gum Day

Tulip Day

Embarrass Your Best Friend Day

Girl Friend Day

Pumpkin Day

Lash Day

Boy Friend Day

African Immigrant And Refugee Hiv And Hep Awareness Day

Hiv Awareness Day