how to set 4 differ color to every 4 next item in datalist

i have a datalist and i am showing many items in it, now i want that set 4 differ color to every 4 item in datalist  and then again repeat these colors next 4 items then again then again and so on,

(without database interaction)

for eg.  20 items in datalist then

1st is red

2nd is blue

3rd is green

4th is brown

then again

5th is red

6th is blue

7th is green

8th is brown 

and so on....

 thanks for any help