Took my engine cover to the Caddy dealer I got it from (now closed by GM) & had it painted body color, then took it to an air brush artist to have the "Northstar" & other sections painted silver. Don't know if your dealer would paint it - my current Caddy dealer said they would never have touched painting the cover because of problems getting the paint to adhere properly. However, my paint job has held up just fine.
I tried to get the Caddy crest on the cover "colorized," by the air brush guy, but I didn't like how that turned out so I just had CarArtwork make a medallion that has "XLR" & the crest & put that where the orignal crest was.
Since then I've found a custom rim shop that will paint most anything & who did a great job on my wheels, so if I had to do it again I would probably take something like that to them. They showed me paint jobs they've done inside other engines.
So, I'd recommend trying your dealer or somewhere like the rim shop. Other folks on here have gone about painting the engine cover in other ways, so there's lots of options.