What happens when two selectors have the same deck colour?
In episode 11 of Selector Spread WIXOSS, There is a same-coloured battle:


    between Mayu &amp; Ruuko (Black vs Black)
 


It seems like when the selectors are battling with the same deck colour, they can choose who goes first.

This also ties into the real game - where there are no hard set rules on which player goes first. (although I presume this advantage is offset in some way)