Hi rsheedy,
I have a 2018 RP178 and I got the color codes for the following colors from Forest River. My understanding is the paint is a custom color from a company called Rollie Williams.
The Blue Blaze is Forest River # FR-1027 (this is the blue paint on the sides).
The Diamond Ice is Forest River # FR-1029 (I believe this may be the grey color you are looking for).
I have the color codes for both so they can be mixed properly from whatever supplier you can find to do this for you. I'm not sure how to attach a picture to this forum, however, if you would like the codes, I will be happy to email them to you.
I was told that to do it correctly, you would have to add a clear coat and hardener after touch up.
I have not used the touch up paint yet, so I'm not sure how well everything will work yet.
I hope this was helpful....