It's getting to be that time again for fans of Wisconsin's fall colors. The state Department of Tourism says less than a quarter of the change is complete statewide, but some northern forests are near 30 percent. Fall colors occur as the amount of daylight decreases and trees produce less chlorophyll, allowing yellow, orange, red and purple pigments to emerge. The Department of Natural Resources says a few frosts in northern Wisconsin over the past couple of weeks have triggered the change there. Department of Tourism spokeswoman Sarah Klavas says color in northern Wisconsin should peak late this month. The peak in central Wisconsin is expected between the end of September and mid-October, and southern Wisconsin will see it in early to late October.