Divide by 255
UIColor(red: 0.227, green: 0.482, blue: 0.835, alpha: 1) is the same colour as rgb(58, 123, 213). Each channel is just its 0 to 255 value divided by 255. 58 divided by 255 is about 0.227, 123 gives 0.482 and 213 gives 0.835.
Alpha is 0 to 1 already, so 1 is solid and 0.5 is half see-through. Three decimal places is plenty - the next digit changes the colour by less than one step out of 255.
UIColor, NSColor and SwiftUI
UIKit on iPhone and iPad uses UIColor(red:green:blue:alpha:). On the Mac, AppKit's NSColor(red:green:blue:alpha:) takes the same four numbers.
SwiftUI has its own Color(red: 0.227, green: 0.482, blue: 0.835), with an optional opacity: on the end. You can wrap a UIKit colour too with Color(uiColor:), handy when a project has both.
There's no built-in way to make a colour from a hex string in either framework. People write little extensions for it, or you can just paste the hex here and copy the Swift version.
The classic mistake
Writing UIColor(red: 58, green: 123, blue: 213, alpha: 1) with the 0 to 255 values. It compiles fine, runs fine, and gives you something that's basically white, because every channel is way over 1. Divide by 255, or write 58 / 255 in the call and let Swift do it.
Since iOS 10 these initialisers work in extended sRGB, so values outside 0 to 1 are allowed on purpose, to reach colours beyond sRGB. That's why nothing warns you when you pass 58.
Asset catalogs
For colours you use all over an app, a colour set in your asset catalog is usually tidier than code. Xcode lets you type a hex value or 0 to 255 numbers there, and you can give each colour a dark mode variant. Then it's just Color("Brand") or UIColor(named: "Brand") in your code.