[Xubera]

change the

chat:SetVertexColor()

to

chat:SetBackdropColor()

edit::

For the onload, just wrap your .lua bit in a function like

function chat_OnLoad()
  --lua stuff goes here
end

and in your XML, add <Scripts> tag

<Frame name="chat">
  ...
  <Scripts>
    <OnLoad function="chat_OnLoad" />
  </Scripts>
  ...
</Frame>

and make sure your .toc loads the XML before the lua