How do I shade plot area with increasing and decreasing shades of a color

Hello,

I want to plot an area of a graph (x = 1:24, y = -1:1) with one color (black), which I then want to decrease/increase in shading in terms of the time of day. So, that I have a plot which is 'dark' in the background at night and 'light' during the day with x being hours of day and y being a value. My sunrise would be at 6.8 and my sunset would be at 22. I would then overlay scatter plots with data on top.

Can someone please help me? I have tried messing around with patch and area but with no luck

[Michael]

Anyone have any ideas?