Hellz to the no on shiny sprites, freak of natures those sprites are
you at least need a team of 4 for Heart of a Legend
if let's say you are using Ho-oh you have to have a fire type on your team, and then a flying type, that would leave you with two colored pokes. The way it works you you pick the most promintant first.
I guess there is some room open for interpretation, but hell the first color I see is orange, so orange Pokemon
The second color that strikes me is that vivid green, so green
Basically you can't get away with stealing the color of Ho-oh's feet or eyeballs because you have to work your way through with the most obvious color, then to the second, and so on