A simple extension to SwiftUI Color that bridges over the "missing" colors from UIColor. Write `Text("Hello").foregroundColor(.label)` instead of `Text("Hello").foregroundColor(Color(UIColor.label))`

Color+UIColor.swift

//
//  Color+UIColor.swift
//  Swatches
//
//  Created by Timothy Sanders on 2019-11-15.

import Foundation
import SwiftUI
import UIKit

/// Color definitions of the UIColor constant colors.
@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
extension Color {
    #if !os(watchOS) // watchOS doesn't support adaptable colors.
    // Adaptable colors
    public static let systemRed = Color(UIColor.systemRed)
    public static let systemGreen = Color(UIColor.systemGreen)
    public static let systemBlue = Color(UIColor.systemBlue)
    public static let systemOrange = Color(UIColor.systemOrange)
    public static let systemYellow = Color(UIColor.systemYellow)
    public static let systemPink = Color(UIColor.systemPink)
    public static let systemPurple = Color(UIColor.systemPurple)
    public static let systemTeal = Color(UIColor.systemTeal)
    public static let systemIndigo = Color(UIColor.systemIndigo)
    
    // Adaptable grayscales
    public static let systemGray = Color(UIColor.systemGray)
    #if !os(tvOS) // tvOS doesn't have the adaptable gray shades, just the primary color.
    public static let systemGray2 = Color(UIColor.systemGray2)
    public static let systemGray3 = Color(UIColor.systemGray3)
    public static let systemGray4 = Color(UIColor.systemGray4)
    public static let systemGray5 = Color(UIColor.systemGray5)
    public static let systemGray6 = Color(UIColor.systemGray6)
    #endif //!tvOS
    
    // Adaptable text colors
    public static let label = Color(UIColor.label)
    public static let secondaryLabel = Color(UIColor.secondaryLabel)
    public static let tertiaryLabel = Color(UIColor.tertiaryLabel)
    public static let quaternaryLabel = Color(UIColor.quaternaryLabel)
    public static let link = Color(UIColor.link)
    public static let placeholderText = Color(UIColor.placeholderText)
    
    // Adaptable separators
    public static let separator = Color(UIColor.separator)
    public static let opaqueSeparator = Color(UIColor.opaqueSeparator)
    
    #if !os(tvOS) // tvOS supports the above adaptable colors, but not these. 🤷‍♂️
    // Adaptable backgrounds
    public static let systemBackground = Color(UIColor.systemBackground)
    public static let secondarySystemBackground = Color(UIColor.secondarySystemBackground)
    public static let tertiarySystemBackground = Color(UIColor.tertiarySystemBackground)
    
    
    // Adaptable grouped backgrounds
    public static let systemGroupedBackground = Color(UIColor.systemGroupedBackground)
    public static let secondarySystemGroupedBackground = Color(UIColor.secondarySystemGroupedBackground)
    public static let tertiarySystemGroupedBackground = Color(UIColor.tertiarySystemGroupedBackground)
    
    // Adaptable system fills
    public static let systemFill = Color(UIColor.systemFill)
    public static let secondarySystemFill = Color(UIColor.secondarySystemFill)
    public static let tertiarySystemFill = Color(UIColor.tertiarySystemFill)
    public static let quaternarySystemFill = Color(UIColor.quaternarySystemFill)
    #endif // !tvOS
    #endif // !watchOS
    
    // "Fixed" colors
    // Some of these clash with existing Color names: compare Color.blue (0.22, 0.57, 0.97) in the light theme to
    // UIColor.blue (0.01, 0.19, 0.97) to see two very different shades of blue. For that matter the adaptable
    // UIColor.systemBlue in the light theme (0.25, 0.56, 0.97) isn't *quite* the same blue as Color.blue either.
    
    //So all of the UIColor "fixed" colors are here with "fixed" prepended to the color name.
    public static let fixedBlack = Color(UIColor.black)
    public static let fixedDarkGray = Color(UIColor.darkGray)
    public static let fixedLightGray = Color(UIColor.lightGray)
    public static let fixedWhite = Color(UIColor.white)
    public static let fixedGray = Color(UIColor.gray)
    public static let fixedRed = Color(UIColor.red)
    public static let fixedGreen = Color(UIColor.green)
    public static let fixedBlue = Color(UIColor.blue)
    public static let fixedCyan = Color(UIColor.cyan)
    public static let fixedYellow = Color(UIColor.yellow)
    public static let fixedMagenta = Color(UIColor.magenta)
    public static let fixedOrange = Color(UIColor.orange)
    public static let fixedPurple = Color(UIColor.purple)
    public static let fixedBrown = Color(UIColor.brown)
    public static let fixedClear = Color(UIColor.clear)
    
    // There are a few more predefined UIColors that could go here. groupTableViewBackground is formally deprecated
    // in favor of systemGroupedBackground so I didn't include it. lightText and darkText are not formally deprecated,
    // but there is a comment recommending replacing them with label and related colors so I didn't add them to this
    // list.
}

This shouldn't be used since the color changes dynamically between dark and light mode, but the let makes it such that Color's value remains tied to the one computed the initial time (before colorScheme change).

Color.red and UIColor.systemRed (and others) are the same.