readme-color-changer.sh

#!/bin/bash

# Array of options
colors=(000000 ffc857)
num_colors=${#colors[@]}

# Find current title color
cur_value=$(sed -n -e 's/^.*title_color=//p' readme.md | cut -c 1-6)

# Get index of current title color in colors array
for i in "${!colors[@]}"; do
   if [[ "${colors[$i]}" = "${cur_value}" ]]; then
       cur_index="${i}";
   fi
done

# Get next index in array (looping back if too large)
next_index=$((($cur_index + 1) % $num_colors))
next_color=${colors[$next_index]}

# Find and replace within README
sed -i .bak "s/title_color=.\{6\}/title_color=$next_color/" README.md