The process of installing this is easier than you'd think, I'd personally follow the IFixIt guide for disassembly and reassembly (Up to Step 10, Step 11 & 12 are unnecessary for this). I would heavily recommend printing this with a resin printer as it can handle the small parts as well as make it very smooth from the get go.
As far as the coloring I printed using a clear resin with blue dye (make sure the dye is compatible with printer resin) and then I also painted the inside of it to help it pop more. However if you go with a solid color then you don't need to worry!
To print the other trigger just mirror the trigger in the slicing software.
IFixIt Guide - https://www.ifixit.com/Guide/Steam+Deck+Right+Trigger+Replacement/148900
The author remixed this model.
I cleaned up the interior of the model so that you can print it and fit it without having to modify anything.