I searched the internet for possible solutions but with no luck, I haven't found anything that's really relevant to what I have experienced. With these said, just minutes ago, I figured out what whas wrong and eventually found a simple solution to this problem.
While unpurposefully checking my graphics card settings, I noticed something was really unusual, my saturation has been really set too low (for a reason I still haven't found out). So what I did was to restore the settings to its default, and voila, solution solved. Now I'm having a great time previewing my videos on to mplayer.
I hope this could be helpful to you.
P.S.: I'm not pretty sure if this solution solves other problem where there's a different graphics card installed.
Below are the screenshots of the process (click images for larger view):