matching a rendered color to the preview color

[brooklyn]

hi everyone,
i'm pretty new to ks and am having a pretty fundamental issue.  the problem is this:
lets say i want to render plastic.  i choose my diffuse color, but when it renders, it looks completely different.  it seems to be shifting in color, rather than just being lighter or darker than the preview.  i have tried to adjust the environment brightness and also the settings brightness, but no luck.  also, i dont havent changed any of the other settings in the 'plastic material' dialog box.
when i do the same thing with a 'paint' material, the colors are spot-on.
make sense?  please let me know if you've run into the same thing and if so, how you fixed the problem.

thanks!

[KeyShot]

In KeyShot 4 we have an option to match the color you pick exactly. It will be released shortly.