Bash: for loop with index

#!/bin/bash

colours=(red green blue white)

for ((index=0; index < ${#colours[@]}; index++ )); do
  colour="${colours[index]}"
  echo "- index: $index, colour: $colour"
done

Example output:

- index: 0, colour: red
- index: 1, colour: green
- index: 2, colour: blue
- index: 3, colour: white