That’d be standard swift type inference. The .color function takes a single unnammed parameter of type Color (or similar, idk exactly). Color.gray is a static constant value. So .color(Color.gray) can be simplified to .color(.gray)

Huh, that's actually a great way to do type inference. Swift seems like an excellent language.

That syntax is a shortcut for UIColor.gray, so this is really:

.color(UIColor.gray)

I would expect it's the grey static member of SwiftUI's Color struct:

https://developer.apple.com/documentation/swiftui/color/3049...

I guess .color() is a method, and .gray is an enum case.

that's shortcut syntax for an enumeration case where the type of the enumeration can be inferred

It's not just for enums. It works for any static variable on a given type. So you can say .gray and have it map to NSColor.gray, etc.