I have an issue with exported JPG files from LR4 looking washed out... just wondering if anyone else has experienced this?

I'm using a D600 (NEF) with the latest update to LR4 and ACR, strange thing is when I export an older file (CR2) from my 400D there is hardly any loss of colour LR4 doesn't yet fully support the D600 but how could this be an issue as Nikon have been using NEF files for years!

If anyone has any idea on what the issue could be I would love to hear from you as I don't know what else to try...

Cheers
E