pour

Tap or click a bottle to lift it, then tap the bottle you want to pour into. The lifted bottle pours its top run, meaning every matching layer on top. Colour only lands on the same colour or in an empty bottle. Tap the lifted bottle again, or anywhere off the shelf, to put it down.

You get a partial pour. As many layers move as there is room for, and the rest stay in the first bottle. A partial pour still counts as one pour.

A full-size bottle holding four layers of one colour is finished. A cap drops onto it and it is done for the rest of the level, so nothing pours out of it or into it.

Small bottles hold only two layers. They are handy for parking a colour while you dig underneath, but they can never be finished, so they must be empty again before the level counts as solved.

A frozen bottle shows a number, the pours left until it thaws. Until then nothing pours into it or out of it. It cracks open on the pour that reaches zero. Undo a pour and the ice comes back, because the thaw follows the pour count.

A padlocked bottle carries a lock in a colour that is not inside it. Finish a bottle of that colour and the lock springs open and stays open. Until then the bottle cannot be poured into or out of.

Hidden layers. You see the top colour of the bottle, but the layers under it show as grey until they reach the top. They are only hidden from view: if the layer below the top matches, it pours along with it.

Par is how many pours the solver needed. Finish at par or under, with no hint and no spare bottle, for three stars. Finish within about a quarter more than par for two stars. Any other finish earns one star.

Five on easy, three on medium and one on hard, per level. An undo puts back the last pour exactly, including any ice it thawed. Undo does not lower your star rating, but the pour count it restores is what counts.

A hint asks the solver for the best next pour from where you are and outlines the two bottles with an arrow, with an estimate of the pours left. You get three on easy, two on medium and one on hard. Using one rules out three stars.

Once per level you can add an empty full-size bottle to the shelf. It often gets you out of a tight spot or a dead end, but a level finished with the spare bottle tops out at two stars.

Easy has four or five colours, two empty bottles and nothing hidden. Medium has six to eight colours, small bottles from level 3, hidden layers and frozen bottles from level 5 and padlocks from level 9. Hard has nine to twelve colours, hidden layers everywhere and frozen and locked bottles from the start.

Every UTC day there is one shelf per difficulty, the same for everyone. Your first finish is the scored one, ranked on fewest pours and then time. Later attempts the same day are marked as practice.

Yes. Turn on shapes from the start screen or the bar under the shelf and every colour gets its own small symbol, drawn on each layer, on the stream while it pours, on caps and on padlocks. The setting is remembered.