Color Theory: How would I make this physical item appear black, yet allow as much light through as possible?

I have a calculator-like solar cell that I want to appear black by placing some kind of filter on the front. I would like to make the white lines less apparent, and the brown a darker color. My only option is placing some kind of transparent filter on the front.

How would I go about thinking through this problem, and the color I would use? I was hoping there was a more mathematical way to solve this problem, such as "Well, if you put a green filter on the front, it would look more black". My concern is that placing a green gel on front... isn't that a band-pass filter and it only allows green to get to my solar cell? That is horribly inefficient... Any thoughts or ideas?

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