ADoes anyone know of a good tutorial or could describe how to do mosaic technique on buttercream... I woulr really appreciate the help :)

You could use colored piping gel...it will sort of look like stained glass. 

http://cakecentral.com/g/i/2964952/my-first-attempt-at-stained-glass-done-on-buttercream-icing-using-mycakeschool-com-and-melissas-tutorial/

Here is a picture of the stained glass technique on buttercream.