I would still use a dark chocolate glaze - because a white one might look “off” against the chocolate shell - it may look more ghostly depending on how opaque it is or isn’t; you could always put a white line (stripe) for contrast) or perhaps some cocoa powder.
For coffee extract, you could take some powdered espresso (like Medaglia d"Oro, it’s an instant coffee granule) if you have it in your area; you might have a coffee extract recipe in your pastry school book of recipes; add it to the finished creme pat to taste. If you don’t have a powdered espresso, you might be able to find the stuff that Starbucks sells called VIA, I’ve been using it to flavor simple syrup and it works nicely.
Either of the powdered coffees are very fine, but you will find it easier to incorporate if you dissolve it in a small amount of water - just a few teaspoons because you want it to be concentrated). I used the VIA today to do the simple syrup when we were soaking rounds of biscuit making individual chocolate velvet mousse cakes, I think one of the packets is meant to be used in 8 oz of water if it was for drinking, but you would only use barely a tablespoon of water to dissolve one of those packets in to flavor your creme pat.