The Americolor ivory (available on this site), is a really beautiful, true ivory shade - some (like Wilton's), I find to be too yellow. Hope that helps!
Are you making the sugarpaste from scratch, or using pre-made and coloring?
If you are making it from scratch, add some vanilla or a touch of brewed orange pekoe tea in place of water to get ivory. Double bonus - the vanilla will flavor it.
If you are using pre-made sugarpaste, use the lightest brown you can get, and use it sparingly. Remember, brown will darken as time passes, so make it a little lighter than the shade of ivory you are seeking, and wait an hour or so to see what happens. You may need to add a touch of gold or yellow to achieve your final color.
Theresa 
I agree then, the smallest touch of brown with the tiniest bit of gold (or golden yellow) should get you a nice colour. If you look in my photos, there is an art deco cake that was done with fondant I coloured using this method to get a cream/ivory colour. Hope that helps!
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