The bind that Solarverse provided in a sense, works, but broken. The changes, if memory serves right, was 'fixed' on Issue ...either 16 or 17. Reason for the change was that players were able to post false powers/abilities link, clicking on it could result to anything that could be done with the slash command.
Back on topic, if one must really want the clear background, following the command as an example:
/bind enter "beginchat <color white><bgcolor #0000001><bordercolor white>"
You'd have to keep moving the cursor every single time at the end before typing... or, just copy paste the color input before typing your message.