Color Balance and Time of the Day
Early morning and late afternoon light outdoors produces a warmer, more reddish color balance than you will get at midday.
In photography, there is a color of light called "daylight". However, over the course of the day, the light can change from a warm red at sunrise, to a cold blue at noon, and then back to a warm red or orange at sunset. "Daylight" on the color temperature scale is really set for midday sun between 10 A.M. and 2P.M on a clear day. During these hours, colors appear clear, bright, and accurately rendered in the photo.
Before and after midday, light from the sun is modified by the extra distance it travels through the Earth's atmosphere. Some of the blue light is filtered out, leaving the light with a more reddish cast than at midday. This is easily seen very early or late in the day when the light is often quite red-orange in tone. The change in color will affect your pictures strongly, but this reddish cast is a wonderful light to photograph in.
Just before dawn and at dusk(top), colors often appear muted or monochromatic. During these hours when light is relatively dim, you often have to use an extra-long exposure time.
Midday light on a sunny day(bottom) produces colors that appear natural and accurately rendered.