I recently applied an IPS modkit on my DMG Gameboy. In IPS ready shells, there is a LED diffuser included, because on the IPS board the power LED is a SMD component.

When playing in darker areas I noticed that on the lowest IPS brightness setting, the power LED annoyed me with it's brightness. So I modeled the diffuser in tinkercad and tried out different filaments. It's hard to capture this on camera but as you can see on the comparison picture, there are some differences and I think you just have to try out filaments yourself until you find one that you like. I can recommend bright or slightly transparent ones.

https://www.tinkercad.com/things/6szujRQUOoR-gameboy-ips-shell-led-diffusor