Different leagues, different sports, different rules. In some sports -- soccer being one -- you'll even see hoops or stripes. Most high-level clubs even have third kits, presumably to avoid any/all color similarities. Though I suspect it's more of a marketing ploy.
Given limited budgets in H.S., it should simply be an agreed-upon standard: i.e., white home, dark away, or vice versa.
And, FWIW, home teams should ALWAYS bring BOTH, in the event a "road" team shows up with the wrong unis.
