In runescape how do you change text color?

It's very simple to change the text colour. You simply use this format:

[color name]: [message]

White: Hello!

Would give you white text, saying "Hello!"

This format works for Yellow, Red, Green, Purple, Cyan and White. You can also use special "effects", which use the same format:

[flash1/2/3]: [message]

[glow1/2/3]: [message]

[scroll]: [message]

[shake]: [message]

[slide]: [message]

[wave1/2]: [message]

You can also combine these codes, such as Cyan:Wave: [text]