You see this colour graduation in nature all the time, my favorite is the way hydrangeas fade from dark to light.
I really think flowers do it best. Oh & sunsets they do it really well too, I guess sunrises too but I don't do mornings very often, so I'll let you be the judge of that.
There are some awesome tutorials on the web that show you how to achieve this effect.
These pic are from pintrest.com
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