Text colors can be added to chat windows by using Hex Color Codes. This is done by placing the hashtag and six digit hex code inside brackets: [#229954] is green, for instance. If you add them to the in-game chat, the brackets & hex code will color any text that follows that color.
see https://htmlcolorcodes.com/color-chart/ for colors
To add emojis to your chat, add the following tags with a colon on each side to whatever you are typing: