second 2 elements of seventh element of hextets converted into hexadecimal number, first 2 elements of eight element of hextets converted into hexadecimal number, second 2 elements of eight element of hextets converted into hexadecimal number. join first 5 elements of hextets into a string, separated by ':', substitute the result for result.
result = ':' . join ( hextets [ 0 : 6 ] )