Wallpaper Colour Issues

[littleb2005]

i have a wallpaper which is ok tile it

but when i strech it i go all werid

http://chiddy.pwp.blueyonder.co.uk/1/desktop.png this is the picture streached

and here is it tiled or here what it should like like

http://chiddy.pwp.blueyonder.co.uk/1/desktop2.png

anyone got any idea running on an imac 28inch here