ive seen it before. it got me the first time i did one, but then i payed attetion the next time a figured it out.
it a simple deduction problem. when you pick your number, each number is broke down 5 to a color. well when it ask you what color your number is, it already knows what 5 numbers to go after. then when it says pick the set of numbers out of the 5 blocks later, each of the 5 from the original color are seperated, one number for each box. so when you click it, it doesnt matter what ball or door you choose, it will be behind the door reguardless.