IMac screen turned into a negative effect.. HELP

[mighty30]

i dont know if this is the right spot but ...I have an IMac and today when i woke up I found my screen turn to a "negative Look" so now eveything is in that effect even when I watch videos its in " negative effect" this is frustrating . How do I fix this?

 

[Kaveman]

This is for those with Sight problems.

Apple Menu > System Preference > Universal Access > Seeing > Display

or the keyboard Chord
Control - Option - Command - 8