bouncybunny - 11:16 am on Dec 12, 2008 (gmt 0)

I also think this sounds like the "Only Web Colors" checkbox is selected (or not as the requirement may be).

Gamma shouldn't be an issue if the colour picker has been used, as the measurement will have been read 'mathematically'.

And yes, if you export as a gif, you need to ensure that you have allowed enough colours.