It's not that hard really. The tricky part is calibrating the needles afterwards, something I haven't done myself.
The sanding/painting is simple.
Here's what the background area looks like after sanding:


You may see a few remnants of green where I had them painted green at one time.
Just mask off everything you don't want painted the 1st color & spray a few coats, let dry & shine a bright flashlight behind them to simulate the white led's & keep spraying that color until you're happy with the color.
For the 2nd color, unmask that area & mask off the 1st color so as not to overspray onto it & repeat.

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