sometimes it's blurred & turned to a bluish or yellow-green colour, though immediately it becomes normal.

I experienced this thing first while using TuneUp first time.

I have set colour & brightness in amuch lower level. Is this the reason behind this problem?

Answer:
brother don't get upset

check your monitor cable its loose please attach it with CPU tightly than your problem is sort out

after this its again happens than diagnose your monitor

Answer:
-check the monitor wire cord all pins are there or sm are broken or bend

-reinstall motherboard drivers software if there’s motherboard driver err

-if ur using graphic cards or 3d graphic card then remove it and again put it

-any printer is connected? becoz same happens with me when i just on my printer my pc screen become blur for 2-3 sec then become normal

so i just turn off printer and only on it when needed

Answer:
Try using another monitor to see what happens. If the problem persists, it could be a graphics card/driver issue. Now if the problem is only with this monitor, it could be malfunctioning and needs repair or replacement.
Answer:
it has some hardware problem
Answer:
if you are runing vista thats propaly the first stage of the BLUE SCREEN OF DEATH