Rainbow lets any suit follow another in the tableau. Four starting cards sit above a thirteen-card reserve, while a draw-one stock supplies the other 35 cards.
The reserve takes the next empty space
Build descending runs by rank, ignoring suit and color. An ordered rank sequence can move together. Whenever a column empties, the next reserve card fills it automatically. Once the reserve is gone, any card or legal run may fill a space. Foundations build from ace to king by suit.
Watch what a cleared column will reveal
The stock allows only one pass. Check the exposed reserve card before emptying a column: its automatic arrival may create a receiver or interrupt your plan. Playing the current waste card can uncover an earlier one; drawing again will cover that opportunity.