She is scheduled to appear at the Norway restaurant for breakfast. She stands near the entrance for photos and does not circulate. Lunch and dinner Ariel is scheduled to be at the entrance (with belle in her blue dress circulating) but of course the schedule is always subject to change and some have reported being lucky and seeing Belle in her yellow gown at dinner.
I've also heard that she can sometimes be found in her yellow gown in Paris and also in the Toontown tent in MK.
She was in her blue dress at our Princess breakfast in Norway. WE saw her in the parade in a gold dress, but never saw her for autographs in the gold one.
We have only seen her in her blue dress. She was at Norway, in France (with the Beast), and at Belle's Storytime by the castle. I highly recommend the storytime. She is soooo sweet.