Just like WoW, the Diablo 3 chat UI accepts commands to change the color of your text and include icons as well. While you can use predefined colors such as red {c_red}your text goes here{/c_red}, you can also use aRGB values to use any color you wish.
The image above includes:
{c:FFFF00FF}It’s salmon, not pink!{/c}
{c_rare}Rare Item{/c_rare}
{icon:gold}
Here is a list of some that have already been data mined.
Predefined Colors:
{c_magic}text{/c_magic}
{c_inferior}text{/c_inferior}
{c_rare}text{/c_rare}
{c_epic}text{/c_epic}
{c_legendary}text{/c_legendary}
{c_questlog}text{/c_questlog}
{c_whisper}text{/c_whisper}
{c_bonus}text{/c_bonus}
Icons:
{icon:lmb}
{icon:rmb}
{icon:bullet}
{icon:audio}
{icon:platinum}
{icon:gold}
At the current time, these can only be used in the chat window on the left of the UI and not public chat channels found on the right side. It might be possible for players to create macros outside of the game and then call on them within the game for quick and easy access but it’s unknown if this would break the T&C’s and isn’t recommended until more is known.
Whether you love or hate pretty chat, you may want to be prepared for a boatload of it once people figure out even more nifty ways to stand out.