The colors and textures of the Palouse hills are primarily influenced by the variable weather and the crops that blanket the fields. While there's a general progression of changes in the appearance of fields over the course of a year, part of the fun of photographing the Palouse is that these patterns aren't set in stone and you can never be exactly sure what you'll see or what the light will be.
Even though the Palouse region isn't very large, there are variations in how the geography and weather affect the appearance of the landscape in different areas. Broadly speaking, the southern and far western Palouse progress through the farming seasons earlier than the central region, with the northeast usually progressing at the latest. The northeast generally holds snow on the ground longer (some years into late February or March), while parts of the south may receive very little to no snow. Also, the lower elevations of the river canyons are drier and rockier and have longer periods of gold and brown tones than the higher elevations. The far western portion of the Palouse (from around Dusty, Washington, and the West) is also drier, less populated, and less treed.
Generally, photographing the Palouse in the early morning or late afternoon-early evening provides the best light needed for showing off the shapes of hills and textures of fields and barn wood. Low-side lighting on the hills at these times creates shadows that make the hills more visible and dramatic.