A couple logs back, I discussed the diffusion problems.

There are two main issues:

The side-mount LEDs only being soldered onto the top layer of the PCB only really allows one colour of LED to show on each horizontal hemisphere, and the vertical resolution is poor, with many gaps.

This is illustrated best with just the blue channel active:

With both, it's still visible but (another issue) the current limit for both LEDs is equal, making the more-efficient green LEDs way bright and blowing out the exposure:

So how don't we fix this issue?

I've got a bunch of PVC tube that slides over the edge perfectly.

It doesn't curve around the edges, though.  Sticks out to the side and is inconsistent and gross.

I tried putting some slits in it to allow it to curve, but they're inconsistent and gross.

Logical next step?

Fire.

Protip: the decomposition products of PVC are chlorine gas! Do it outside! Hold your breath! Nasty stuff.

Also, it didn't work. At all. It's consistently gross.

Next plan.