Spread sixteen piles instead of twelve, build down in alternating colors only, and win by draining the whole stock into columns you keep clearing.

Sweet Sixteen Solitaire is a wide, fast-moving member of the Trusty Twelve family, spreading sixteen tableau piles across the table instead of twelve. Each pile starts with a single face-up card, and the remaining thirty-six cards sit in the stock, ready to refill any column you manage to empty.
The one rule that sets it apart from Trusty Twelve is how you build: here you go down by alternating color rather than by any suit, so a red nine only accepts a black eight, and a black eight only a red seven. That tighter constraint makes each move count, and the whole game becomes a hunt for the right color at the right moment.
You win by emptying the stock completely, feeding its cards into vacated piles until none remain. There is no foundation and no waste to lean on, so success depends entirely on how well you keep columns clearing and refilling in a steady chain.
If you like Sweet Sixteen, try Trusty Twelve Solitaire and Knotty Nines Solitaire, its nearest relatives in the same family.
If you run into anything odd or have an idea that would make the game better, please contact me.
Enjoy playing!
16 tableau piles: Each is dealt one face-up card at the start. Build down in alternating colors, moving one card at a time. When a pile empties, it is immediately refilled from the stock.
Stock: Holds the remaining 36 cards. It never deals onto the tableau by itself; its only job is to top up piles you clear. There are no redeals.
Sweet Sixteen has no foundation piles. You are not building suits up to the King. Instead, the goal is to work the entire stock out through the tableau, so every card in play is about clearing and refilling columns rather than sending cards to a foundation.
Sixteen tableau piles, each beginning with a single face-up card. Only the top card of each pile is available to move.
A card can be placed on a tableau pile only if it's one rank lower and the opposite color of the pile's current top card, so the only cards that fit on a 9 of clubs are the 8 of hearts and 8 of diamonds. Only one card is moved at a time; sequences are not permitted.
When a tableau pile becomes empty, it is automatically refilled with the top card of the stock. Keeping this cycle going is the heart of the game.
The stock keeps the 36 cards not dealt to the tableau. You do not turn it over to a waste pile; instead it quietly feeds the top card into any tableau pile you empty. You win the moment the stock is exhausted.