counting the number of characteristcs selected.

Hi i am having a proble.we are implimenting VC.and we have a characteristic colour. And it has around 22 characteristic values. the customer has the option of choosing the any number of colors. depending on the number of colors selected by the customer the BOM changes.

so i need to count the number of characteristic values choosed in the colors characteristic.

and also is there any way to restrick the customer from choosing not more than 6 characteristics.