I'm working on a composition whith white background ... but after rendering in format such as WMV, and playing this video on different players, the white background look soft grey ! any idea about this problem ?
- broadcast safe colors
- general Gamma adjustments done by your player
- general Gamma adjustments due to color profile (mismatch)
- limitations in the chosen CoDec/ compression
Pick whichever is most likely. For most MPEG derivatives and WMV a color space compression is normal and unfortunately you cannot override these behaviors from within AE in most cases. You will have to use other tools. It is however absolutely possible to improve color perception by adjusting the colors before the compression. I recommend you check out The Meyers' tutorials on broadcast safe treatment or Aharon Rabinowitz podcast on creativeCOW to learn how expanding and compressing color ranges can improve perception and technical quality.