You can use the following format to give in-game broadcasts color.
The following uses Ark Markup Language
.rcon <cluster> <map> broadcast <message>
.rcon pvp rag broadcast <Rich Color="0.5,0,0.5,1">Hello World!</>
| Color | Format |
|---|---|
| Red | <RichColor Color="1,0,0,1">Red</> |
| Green | <RichColor Color="0,1,0,1">Green</> |
| Orange | <RichColor Color="1,0.65,0,1">Orange</> |
| Black | <RichColor Color="0,0,0,1">Black</> |
| Yellow | <RichColor Color="1,1,0,1">Yellow</> |
| Fuchsia | <RichColor Color="1,0,1,1">Fuchsia</> |
| Purple | <RichColor Color="0.5,0,0.5,1">Purple</> |
| Blue | <RichColor Color="0,0.5,0.5,1">blue</> |