Yes, I have noticed some DVDs have a slightly washed out color to them as well when using the Windows 7 players.
I usually rip all mine to MP4 or MKV files, either as a compressed file or sometimes untouched. I find the picture quality just looks better on the PC.
It resolves the washed out look.
I also prefer this method using librarys VS swapping DVDs in and out.
As for you initial question however, you may try adjusting the color settings in your player, or through your Graphics card. (The AVIVO Video setting in Catalyst for ATI cards)
I found setting the player to use Hardware Acceleration, and then making a few tweaks in AVIVO solved DVD playback (washed out) issues for me.
This would be my recommendation.
I use NeroShowtime as my default movie player for files and DVD alike however, so Im not exactly sure if this helps with other Players.