Hi, i downloaded the trial and played it for the time i had and everything was alright.
But then i bought the full game and when i run it, it shows in inverted colors.

What should i do :S?

Try http://forum.team17.co.uk/showthread.php?t=36539 and/or http://forum.team17.co.uk/showthread.php?t=36535 . Before that though, try the common tricks in the Right click, properties, compatibility tabs of fiddling with the settings, especially disable aero effects, run in 256 colours, and compatibility mode. Also try keeping C:\Team17\Worms World Party open in explorer when you run the game (sounds crazy but works for some)