Rules clarification: {X}, as in {8} seen in Koz's card, can be paid using any color of mana but
, let's call it {C}, can only be paid using a colorless source which gets a little confusing.
Because for the purposes of generating, {1} mana equals {C}. But for the purposes of expending {1} can pay for {C}, {R} can pay for {1}, but {R} but it
cannot pay for {C}. Confused yet?
Since official MTG is not allowed to add a 6th color they basically started using colorless as a pseudo-color and claiming colorless isn't a color.
The better way to think of it is {1} is now called "any", as in any type of mana can be used to pay for it, be it {R}, {W} or {C}. And in turn, all colorless sources are now called {C}, and {C} is the only thing that can pay for {C}. Throwing the word "colorless" around is essentially meaningless and confusing thanks to MTG's deva team drawing lines and technicalities to create new dynamics.