This ShapeStyle extension helps you to use your custom colors in a very easy way

CustomColorExtension.swift

import SwiftUI

extension ShapeStyle where Self == Color {
    static var darkBackground: Color {
        Color(red: 0.1, green: 0.1, blue: 0.2)
    }
}

// HOW TO USE IT
struct ContentView: View {
  var body: some View {
    Rectangle()
    .fill(.darkBackground)
  }
}