Free chat plugin sidebar

Hi,

I’m looking for a free chat plugin that doesn’t slow down my website. I don’t need it to be on the homepage. I would like to have in on pages and the sidebar. I also don’t need a chat room, only to answer clients individually. It would be good to be able to change the colors and add a picture. I would appreciate if somebody can give me an option..I’ve tried many but can’t find what I’m looking for.