In order to use hex colors first get your desired color's hex value (for example the hex value of a color with RGB value 70, 180, 95 would be 46B45F. You can use online converters to get hex value). Now that you have your hex value, you can use it as follows for text plain messages: '&x&4&6&b&4&5&f' (Insert '&x' and then your hex value but insert & before every character of said hex value). For JSON messages, insert '#<hex value>' in the color section.
Default configuration has been updated to show usage of hex colors support.
Thanks to
@HexedHero for motivating me to do this.