I remember as a kid there was an older local kid that had a gray and black 73 Mach and that car was beautiful. I agree with you in thinking there's something about the shape of the 69 and 70 cars that they need a different color on the hood at least, unless they are black or have a Boss 429 scoop on the hood. I remember Calypso Coral being a crazy color, but the images that come up on an internet search just look more normal red to me. I don't see anything wrong with choosing red. It's not my first choice but also not my car!
Gulfstream Aqua is a great choice I agree. Gray/black usually looks good, but there are a lot of Eleanor cars that got painted those colors, don't know if you care about that.
I've been dreaming about painting my 70 for many years, but I need to fix the body first. I always think I'd like some darker metallic green similar to a Bullit color, but still I think the car will need black on the hood. Either that or just keep it black like it currently is. My car was born in Forest Green - I hate that color but it makes me want to use some shade of dark green. What color did your car come from the factory with?