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I have the following code to convert RGB to HSV. This uses UIColor which is part of the UIKit. UIKit is not available in macOS. What is the alternative to do this in macOS?

func getHue(red: CGFloat, green: CGFloat, blue: CGFloat) -> CGFloat 

 let color = UIColor(red: red, green: green, blue: blue, alpha: 1)
 var hue: CGFloat = 0
 color.getHue(&hue, saturation: nil, brightness: nil, alpha: nil)
 return hue

In macOS, use NSColor instead UIColor.

func getHue(red: CGFloat, green: CGFloat, blue: CGFloat) -> CGFloat
 let color = NSColor(red: red, green: green, blue: blue, alpha: 1)
 var hue: CGFloat = 0
 color.getHue(&hue, saturation: nil, brightness: nil, alpha: nil)
 return hue

You should be using NSColor on macOS instead of UIColor. The two are similar, though NSColor allows for better color management, should you need it. It includes a similar getHue(_, saturation, brightness, alpha) method.

I would implement this a bit differently:

import AppKit

extension NSColor 
 var hsba: (hue: CGFloat, saturation: CGFloat, brightness: CGFloat, alpha: CGFloat) 
 var hue: CGFloat = 0
 var saturation: CGFloat = 0
 var brightness: CGFloat = 0
 var alpha: CGFloat = 0
 self.getHue(
 &hue,
 saturation: &saturation,
 brightness: &brightness,
 alpha: &alpha
 )
 return (hue, saturation, brightness, alpha)
 

This lets you easily access not just the hue, but the satuation, brightness and alpha as well. And it doesn't require you manually provide 3 seperate rgb components. You can just call it on any existing NSColor instance. You might initialize one using rgb components, but you could also use any other other NSColor instance, such as one returned by another API, or one of the static value like NSColor.blue).

print(NSColor.green.hsba.hue)