Although colour blindness prevents someone from identifying colour, that doesn't keep them from seeing the evidence of their existence. Even for those most affected, the varying shades of grey indicate a spectrum. Without experiencing it, a colour blind individual knows it's there.

You don't have to be a talented puzzle-solver or gaming savant to appreciate the vibrance of Primrose. A few short minutes with this brilliant puzzler is enough to recognise its potential for short sessions or long strategic plays.

In short, it's a beautiful, sophisticated game characteristic of the innovation engendered by the iPhone.

Primrose can run and run, with scores posted from around the globe running into trillions, players presumably dipping in and out of this grid-based puzzler long into the night.

Starting out with a clear 7x7 grid, Primrose has you place coloured blocks in groups of two with a tap of the screen. The second square has to be placed in a slot that runs in line with the first - either horizontally or vertically - with the game highlighting potential spaces with a marker.

Your aim is to surround squares of one colour with squares of another, dissipating the ones trapped in the middle and transforming those around the edge into the colour of the squares you've just cleared from the screen.

Plan your moves well and you can set off chain reactions, with swathes of the board disappearing or changing shades in a snake like motion that has an altogether positive reaction on your score.

Given three colours to start - purple, light green, and orange - the number grows as you advance in Primrose. Greys, reds, pinks, and darker greens appear later on. Once the screen is filled with the colours of the rainbow, your available choices become very limited.

You can easily run yourself into a corner after just a few minutes' play, making those first steps the most important.

It's in this way that the game's difficulty plays out in waves. Once you've ridden that storm, you then have to contend with chains of squares of the same colour being presented to you.

Their placement is particularly tricky since you risk clogging up the entire map with squares of just one colour. It's the kind of test that can finish off a game that's been teetering on the brink from the outset.

On the other hand, it's perfectly possible to play forever and a day, totting up fairly mind-blowing scores that put the rest of the world to shame. Primrose has the perfect balance of casual play and hardcore strategy that could and should attract gamers of all creeds.

It also has a handy colour blind mode that labels each square with a letter for added distinction. That in itself is merely a small gesture, but it perfectly illustrates how tiny touches added up into an enduring package that's perfect for either a quick dip or long haul.