Freeware: F.Lux For Windows And Linux
f.lux makes your computer screen look like the room you're in, all the time. When the sun sets, it makes your computer look like your indoor lights. In the morning, it makes things look like sunlight again.
Tell f.lux what kind of lighting you have, and where you live. Then forget about it. F.lux will do the rest, automatically.
It is difficult to capture the effect in a screenshot [I have tried several times] I guess the best approximation is that it gives a slight sepia tone to your display later in the day but then I am colour-blind and I sometimes find it difficult to judge subtle differences in tone and colour.
Link: F.lux: software to make your life better