Nobody knows if they're playing Hold'em or Omaha Hi/Lo until the flop lands.
Button and blinds.
Two hole cards, a small-bet betting round, then a three-card flop.
Small bet preflop. Majority-red flop keeps it Hold'em from there; majority-black flop deals two more hole cards and switches to Omaha Hi/Lo 8-or-better. Small bet after the flop reveal either way, big bet on the turn and river.
Scored under whichever game the flop color locked in.