Hey @wildcatter 264 - welcome! You have a few options, if you are wanting to paint your fiberglass roofcap and/or bezel.
The fiberglass roof cap was not painted, but is a resin that makes it the color that it is, however, most people end up painting it cignus white (or budget folks grab ford's wimbleton white, a close match) which is readily available at a paint shop, or can be ordered in rattle cans. My recommendation is a base/clear of T012 - Cignus White. You'll need probably need one quart (half gallon sprayable, with reducer) for the job, plus clear. That'll get your top and bezel looking snappy.
Last, depending on where your 78 is sourced, you may have a metal roof, as I've seen all manner of different types of cruisers being imported with various tops and retro-fits on the trucks. However, chances are you have a fiberglass top that has a riveted steel lip all the way around, and a riveted gusset that bolts to the top of the windshield frame.
While the search function would have answered your question, don't hesitate to ask, as you'll never know what you might learn in doing so.
Have a great weekend.