I have a newly tiled shower that was put in with a metal edging piece.
However you can still see the edge of the cement board underneath it where it meets the wall.
How do I finish this?
Shower – How to finish edge of tiled shower with metal outside drywall
showertile
Related Solutions
I'm just a motivated DIY guy, but when I learned tiling I was told to use silicone caulking wherever tile changes directions. So, inside corners, meeting the floor, etc.
Joe, sorry to use the "answer" function again instead of adding another comment, I wanted to attach more pictures.
The tile I used was not available with a bullnose so I finished it flat on the sidewall. The edge cant be seen normally so I did not spend time making it perfect, but for your situation I retract my note about never finishing an edge with caulking. If you end flat to the wall around that corner it would be perfectly fine to use caulking for aesthetic purposes, use paintable caulk so you can paint a straight line down the whole side when you paint the wall.
Sorry I misunderstood your question, my situation was similar to yours and wrapping the tile around to the outside seemed like the best solution for me, and it looks pretty good that way (at least my wife did not complain, that's all that really matters). 
Related Topic
- Drywall – repair drywall in the shower
- Shower – Kerdi Board at edge of shower
- Drywall – How should I finish a shower stall at an outside corner
- Plumbing – How to ensure shower handle flushed when replacing shower wall to tiled wall
- Doors – Do shower doors for tiled openings have to fit the width exactly
- Shower – Is grout required behind shower knob trim plate
- Drywall – Cement Board versus Mold Resistant Drywall at Top of Bath Tub/Shower Surround
Best Answer
If I understand correctly, the question is how to finish the 90degree transition where the metal trim meets the drywall.
First, I would clean up the metal trim. Scrape off or use some kind of adhesive remover to remove any residue. You may need to buff/polish it with some fine grit sandpaper.
For the transition i would use caulk, If you feel it may see a lot of moisture then use 100% mold/mildew resistant silicone. (after painting the wall)
If not then a paint-able caulk (before painting the wall) that would be able to accept the paint color you choose for the wall.