Love RGB LED strips for home illumination.
Hate the blinding bright spots.
Think that commercially available diffusers being more expensive than the light itself is ridiculous!!!!

This might be a solution for you.

I have designed it as individual segments, since my setup has a lot of twists and turns. But I have included the original sketchup file so modify to your need. In order to get smoother curves, the sketchup design is 100X. Each segment is about 2 grams so barely any material used

I can print a batch of 30 in about 8 hours. Can speed it up but since the walls are really thin(1mm) decided to keep the speed low. Use a tiny bit of clear double-sided tape on either end to mount.

Have fun