I wanted to create a sign with back light
After some different prototypes I came up with this model
NOTE: I have change the dimension in cura.

NOTE, I have resized some of the dimension in Cura.
Bottom is resized to 68x64x2 mm, same size as my LED light panel.
Front is resized to 68x64x6 mm. The height determent the height on the letters/tekst
The shell is in correct size.

The base is an DIY "White Light LED Backlight Light Guide Panel"
On top of the LED panel place the 3D printed bottom part, that is printed in a non light transparent filament
Print the front in tree colors. First blue (in my case) in the top of letters/text and last in the print I change to black and then after 0.3 mm black layers i change to white. The black layer is to block the light from lit the letters. The white is the letter color.
Place the front on top of the other parts
Some parts have to be glued together, like the dots in: A, D, O, 8
Then place all parts in the shell.

You will probably could use other kind of back light.