The Iowa DNR reported on Monday, September 30:

Elm, walnut, ash, birch, and cottonwood are changing to yellow.  White ash are turning purple gradually. Sumac are getting red along roadsides and Virginia creeper vines are becoming a pretty red.  Excessive rain and humidity this growing season have caused leaf diseases on many trees which will likely subdue some color.

You can also utilize this fall foliage map.