How to create custom colors using UIColor RGB and hues

Swift version: 5.2

Paul Hudson @twostraws May 28th 2019

Although there are quite a few built-in UIColors, you'll want to create your own very frequently. This can be done in a number of ways, but the most common is specifying individual values for red, green, blue and alpha, like this:

let col1 = UIColor(red: 1, green: 0, blue: 0, alpha: 1)

Each of those numbers need to be between 0 and 1.

An alternative way is to specify color values as hue, saturation and brightness, or HSB. Hue is a value between 0 and 1 on a color wheel, where 0 and 1 are both red. Saturation is how deep the color should be (so 0 is just gray) and brightness is how light the shade should be.

Here's how it's done:

let col2 = UIColor(hue: 0, saturation: 0.66, brightness: 0.66, alpha: 1)
let col3 = UIColor(hue: 0.25, saturation: 0.66, brightness: 0.66, alpha: 1)
let col4 = UIColor(hue: 0.5, saturation: 0.66, brightness: 0.66, alpha: 1)
let col5 = UIColor(hue: 0.75, saturation: 0.66, brightness: 0.66, alpha: 1)

The advantage to using HSB rather than RGB is that you can generate very similar colors by keeping the saturation and brightness constant and changing only the hue – the code above generates some nice pastel shades of red, green, cyan and magenta, for example.