What was the material that coated the nail?why did the color of the solution change?

you do not give much info but I am guessing that you are doing a single displacement ( also called replacement) reaction..by placing an iron nail in a blue solution of the salt, copper sulfate. The iron is a more reactive metal than copper and will displace it from its salts resulting in a nearly colorless ( or very pale green )solution of Ferrous sulfate ( iron(II) sulfate ) and depositing the copper as an orangish slightly shiny coating on the iron nail





CuSO4 (aq) + Fe(0) -------------- FeSO4(aq) + Cu(0) (s)