Slow and somewhat gradual switch between multiple colors (ie for holiday lighting)

I highly recommend @mbishop Holiday lighting app. this should be able to do what you are looking for.

Edit

I thinknit does, but I would reach out to @mbishop . He can help you if it does, or has been very responsive about adding feature requests pretty quickly and working with the requestor to test and make sure thats what they were looking for.