Bright fall colors in the leaves have mostly come and gone throughout the state, but some oaks are still offering glimpses of color. According to the Department of Natural Resources, cool night temperatures destroy chlorophyll quickly, but having temperatures below freezing inhibits the production of red pigments. Also, dry weather can help with more red pigments, as it allows for a greater buildup of sugars in the leaves. And a killing frost destroys leaf cells and the coloration process lessens. Traditionally, south central Iowa is the last region of the state to have bright fall colors for the season.