The box art of Nintendo games from PAL (Europe) territories all have a little coloured triangle on the spines, but in each territory it's a different colour this is to show the region that copy of the game came from,
Some common ones are:
Green = UK,
Pink = Spain,
Red = France,
Light Blue = Italy,
Dark Blue = Germany,
Brown = Australia.
There are 49 different colours (This number is from: UK Nintendo The Official Magazine: Issue 21; 21st Oct. 07 )
As well as geographic region it is also to do with the language of the Box & booklets, though PAL region, as Nintendo games are made in Germany, the Triangles show the region that the game is shipped to.
All PAL games work on PAL consoles; but the DS isn't region locked/PAL and it is cheaper to buy from Europe (and N. America, which lack the coloured triangles and also have a letter based rating system on the art instead of the usual Europian age system), so some shops here in the UK import the games and sell them for full price!
Different colours don't mean rarity or anything to do with if the game is for Girls/Children/etc, as is often stated (on Ebay as well as elsewhere).
Hope this helps people to understand the Mystery's of Nintendo's Coloured Triangles,