Here is a website with lots of colours and codes on:http://www.visibone.com/swatches/hex.html
As RebelYell says, put the code in square brackets [ ] before your text.
I am on iOS and have set up keyboard shortcuts, found under Settings>General>Keyboard>Text Replacement, for 5 different colours to save typing in the codes every time.
Eg. I type SWCB and I get [66ffff] which gives me Blue text.
SWCR gives me [ff0033] which is Red text, and so on.
Have a play around and find out which shades of colour work best.