RRBBYY

Sometimes we invent games. They might involve seeing who can throw a bottle cap into a cup the most times in a row, who can melt a Cadbury's Chocolate Button in his belly button the quickest, or who can hold his hand over a naked flame without weeping.

We dream them up, play them for a few minutes, then discard them back into the universe of ideas and forget about them forever.

RRBBYY is a bit like one of those games, without the disgusting childish stuff. It has the air of a program created in an afternoon by game design students for a project. That's not to say there's anything wrong with it - a good game is a good game, and this one has the advantage of being completely novel. It's just a bit basic.

Here's how it works: you use your finger to slide a chunky, vaguely abstract painting-like pixellated square around the screen while other pixellated squares drift down from the top. These come in red, blue, and yellow, and every time you tap the screen your own square cycles through those colours.

Tap once and it turns blue; tap again and it turns yellow; tap once more and it turns red; then blue again, and so on. The aim is to make the randomly falling squares vanish by sliding your own square across them, which you can only do if your square is the same colour.

If you touch a square when your own square is the wrong colour, you lose a bit of health - and you recover a single percentage point of health for every correct match that you make. If a square reaches the bottom of the screen, you lose a few of the points you've accumulated by clearing the others.

When you first start playing RRBBYY it seems unbelievably elementary, to the point that you're not entirely sure it's a game at all - just a fairly pretty pixel-art tech demo.

There's no particular strategy to what you're doing - nor even much skill. You're just calmly sweeping away the squares, as though clearing confetti off a table with colour-coded cloths.

Because the only penalty for losing a square off the bottom of the screen is the loss of a few points, there's no real sense of jeopardy. You die, not in a panicked explosion, but through attrition by numerous unmoving incorporeal impacts.

The colour-cycling mechanic is initially tricky, but you'll master it very quickly, settling into a steady rhythm: sweep, find space to change, tap, sweep, find space to change, tap, and so on.

However, RRBBYY is deeper than it initially seems. For one thing, as your score starts to mount up the screen gets busier and wilder and the background changes colour, giving certain squares some camouflage. For another, among the raining squares are power-ups that replenish your health, clear the screen, and vacuum up squares of any colour.

You have to engage the vacuum by colliding with it, and - cleverly - until you manage to do that you lose a point every time it touches another square. The bomb, meanwhile, can be set off by other squares after a period of grace, costing you points if you don't get to it quickly enough.

There are also modifiers, among them the Duplicator, which duplicates squares that touch it but will also duplicate you as long as you're healthy enough, giving you an extra block to hoover up for a few more points. If you're not healthy enough, however, you die.

These cleverly conceived modifiers and power-ups, which can help or hurt you depending on how and when you use them, bring some depth to RRBBYY. And its fluid controls and stylish, unfussy presentation make it a pleasure to dip into now and again to see if you can nudge your way further up the (pitifully under-populated) leaderboards.

But these features can only embellish RRBBYY's basic gameplay so far. In the end, it still feels a bit like wiping confetti off a table. Developer Weekend Jelly has had a good idea and made a decent fist of bringing it to life, but this plays like a game in its concept phase. We look forward to seeing the whole thing.