Back before the oUF version the ticker was created in power.lua (from line 78). It was pretty easy to change the colour by editing the colour values in frame.powerBar.ticker.texture:SetVertexColor and frame.powerBar.ticker:SetBackdropColor.
I believe I found the events for the ticker in oUF_RegenTicker, but I can't find how to edit the appearance now.
How would I go about doing this ?

See the color options in v4140.

Thanks!