Question

why does the blue color of copper sulphate fade away on adding iron filings to it

Answer 1

It is because iron displaces copper sulphte solution to form Fe2SO4 and copper metals gets deposite as iron is more reactive than copper .
Fe(s) + CuSO4 (aq.) - FeSO4 (aq.) +Cu(s)

Answer 2

It is because iron being more reactive than copper replaces it which leads to fading of the colour of copper.....