Changing Bar Colors in Chart with VBA

Hi,

I am trying to change bar colour as per value(marks).

if bar value = 0-60 then bar should be red
if bar value = 61 - 79 then bar should be AMBER
if bar value = 80> then bar should be GREEN

I have wright one code but its not working

its colouring to every bar.i have attached excel file with query


Please help me,advanced thanks