ROYGBIV

Thanks guys!!!

But aren't you counting the case where the last three digits are 128?

So then how do you do it?

Thank you!

Wait, won't some of them contain digits larger than 6?

Actually, the answer was 3. I also got 5 initially, but the answer key is always correct. Nice try! But how do you do it?

Is there a way to do it with Shoelace Theorem?