Hi fellas,
We employ a variation of the rule known as the "one-ball condition" which basically states that your ball type cannot be changed during your round. If you start the round with GI-D then you must finish with the same type. Our variation on the rule comes in when you run out of balls. If you ran out of balls during an actual competition you would be automatically disqualified from the event. Instead of going that route we just equip players with the free starter balls. It is a penalty of sorts for forgetting to stock your bag, but it's lot more lenient than it normally would be in a real competition. Currently, color is not considered the same type though there are discussions about changing that.
Normally this rule is used only in competitive play, but since every mode of play on this site is competitive in some way (excepting multiplayer stroke play and solo practice) the rule was applied throughout all modes.