And which version of Vegas?

1) on which system are you comparing? the Mac or the PC? there can be gamma issues.
2) are you using the scopes to measure before/after? (which leads to...)
3) are you importing the rendered footage into the Vegas timeline and comparing to source layer? if not, how are you determining what effect the codec may be having on playback?
4) what codec(s) is being used to render to? (i'm assuming you're using the same codec for both editing softwares, but figured i should check)

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regarding VLC... do not rely on a media player for accurate visual info. QuickTime, VLC, WindowsMediaPlayer, et al, may alter colorspace, gamma, choose a different codec, etc, in the goal of providing smooth attractive-looking playback. That is what they're designed for.

Use an NLE to determine image-quality of video footage. Use the scopes for accuracy.

One thing that's could have a significant impact is the Canon 5D records with luma values of 0 to 255 (cRGB). Of less signifcance but also worth keeping in mind is it uses Rec 601 colourspace

My understand is that Apple used to set their monitors to a different gamma (2.2) than PCs (1.8) so everyting looks unnaturally more contrasty. I'm far from certain if this is still the case or not but certainly step one is to get both system's monitors calibrated the same at least.
Failing that, play each system rendered output on the others.

Bob.

Actually, classic Windows gamma is 2.2 and Mac is 1.8.
Not entirely sure, but I think only the earlier 5D / 7D models mapped to cRGB.

"Then I have my friend do the exact same thing in final cut"
There is no "exact same thing." They weren't rendered using the same codecs.
I think the OP needs to provide some details. Something will become obvious once we know them.

Title of article below: "Why Do Colors in Sony Vegas Look "Washed Out"?

I've always followed the guidance in this article and applied "Studio RGB to Computer RGB" fx to preview window while editing, then remove it before rendering, and it helps guide the color correction:

http://techblog.cineform.com/?p=2959

"Actually, classic Windows gamma is 2.2 and Mac is 1.8."

Darn, I got them the wrong way around and now to further confuse us Apple have changed to 2.2, mostly.

"Not entirely sure, but I think only the earlier 5D / 7D models mapped to cRGB."

Just checked my old faithfull 5D clip and it sure is cRGB, shadows got to -7% and highlightd clip at 109%.
Our 5D MkII sure looks cRGB playing out clips over HDMI to a video monitor. What has happened I believe is most users now set the camera to Medium Contrast to get around this.
The Cineform Techblog that CClub provided the link to is very interesting. I never knew that most other system convert 16,16,16 YUV to 0,0,0 RGB. That explains a lot that's had me puzzled for a long time. No wonder then you can run into grief on some systems with the 5D.

I should add I've interchanged heaps of footage over the years with Mac users and not noticed any difference between how it ends up on tape. I highly suspect the problem is in how the rendered output is being viewed, not the codec or the NLE. Even on the same PC, same monitor, same footage it can look different depending on how the player drives the screen and how the video drivers are setup. Even within Vegas the preview monitor and the secondary monitor on the same LCD can be quite different to look at.

Bob.

" Even on the same PC, same monitor, same footage it can look different...."

Even following the guidance in that post, if I play the same rendered clip with Windows Media Player, then Media Player Classic, then Nero's player, then iTunes/QuickTime, the gamma levels look different. When I render footage for a customer for computer viewing, I always ask whether they'll primarily be viewing the footage via Windows Media Player or iTunes (iPhone, iPod, et al). Then of course you add into the mix Vimeo, or YouTube... whether they're watching on an LCD (likely) or otherwise... it gets crazy.

Hey All---

Thanks for the responses. Unfortunately I am still very confused-- maybe even more so.

I am working on a PC with Vegas Pro 10.

I am exporting uncompressed quick times.

C

So take your uncompressed QT file and play it back on the Mac and take the uncompressed QT file from the Mac and play it on your PC.
How do they compare?
Look at both on both platforms using scopes, what does that reveal?

Bob.

I had the same problem.

If I exported an uncompressed *.avi - it looked fine

If I exported an uncompressed *.mov - it looked washed out, just like how you described it

P.S. I've just tried to reproduce this with v10.0a, but it doesn't seem to be doing it that way anymore - I think it was happening when I was rendering out progressive uncompressed movies from DV Pal or YUV *.avi

I must have found / or switched settings somewhere this time around...

The uncompressed Quicktime template is a bit tricky, there's a quality slider which defaults to 50% and it also defaults to render at your Project Settings instead of automatically at Best

Hey Bob--

So I did that. The QT rendered from Vegas looked washed out compared to the QT rendered from FCP.

I don't know much about the scopes, but they definitely gave different readings...

-C

Well, I usually render to mp4 and it will look different depending on the player. If I play it back in a flash player it looks fine. Playing the same file in quicktime player; it looks washed out compared to the flash player.

Many variables to consider.