question on how to handle graduated pattern

[mark532011]

I am recreating the center of a pinball table. The problem I have is the blue area, I think the background itself is consistent (though it is hard to be sure,) but the squares pattern ranges from almost faded out light blue with small dots at the bottom to dark blue with mostly filled in dots at top. How would you handle something like that, a consistent overlay and some kind of mask?

A larger version of the image is at: https://drive.google.com/file/d/1bnaOdbu...sp=sharing