Why agcl is colourless while agbr is pale yellow and agi is dark yellow

@ lokesh 
we can explain it with the help of two ways 
1- the cations are same , so, the deciding factors are anions only , more the size of anion , more will be the polarisation , and more will be the colour . 
so, the polarisation is more in I- than in CL-   ,, thus agl is coloured . 
2- more the percentage of ionic charecter , the compound are colourless , less ionic percentage the compound are covalent and coloured , 
due to that agcl is colourless and agl is coloured ,. 
HOPE IT CLEARS 
ALL THE BEST ..