BackgroundModifier.swift

import SwiftUI

struct BackgroundModifier: ViewModifier {
    let colour: Color
    
    func body(content: Content) -> some View {
        ZStack {
            colour
                .edgesIgnoringSafeArea(.all)
            content
        }
    }
}

extension View {
    func applyBackground(colour: Color? = nil) -> some View {
        modifier(BackgroundModifier(colour: colour ?? Colours.mainBackground))
    }
}

Usage:

struct ContentView: View {
    var body: some View {
        Text("I love SwiftUI")
            .applyBackground(colour: .orange)
    }
}

Such a great idea, thanks for showing this! 👍