ASH: Green ash leaves turn yellow, but white ash has a purplish cast. The leaves fall after those of walnut trees, but earlier than those of oaks and maples.
BUR OAK: Buff to yellow colors predominate in bur oaks. The leaves remain on the tree and turn brown before falling.
ELM: Elm leaves turn various shades of yellow, with some turning brown before falling, others falling while still yellow.
HICKORY: Leaves turn yellow on hickory trees, then brown before falling.
MAPLE (SOFT): The leaves of soft (silver) maples turn yellow but do not turn brown before falling.
MAPLE (HARD): Brilliant flame red hues are the signature of hard maple leaves. The red pigmentation of some leaves breaks down before falling.
OAK (RED): The red oaks have brilliant red leaves in fall, though the color is probably not as intense as that of some hard maples.
OAK (WHITE): White oaks have a more subdued purple fall leaf color. The leaves then turn brown and often stay on the tree until new leaves begin to grow in the spring.
Source: Iowa Department of Natural Resources