Showing list faces

How do you "show" an individual face in a list? For instance, the following will change the colours of one of the boxes in a list when the button's pressed, but it uses "show box-list", which updates the whole list. How do I update just the box with the changed colour? (I'm assuming this would be faster on large and complex lists.) colors: reduce [red green blue yellow] len: length? colors view layout [box-list: list 200x100 [box 200x25] supply [ if (count <= len) [face/color: pick colors count] ] button "Change" [ change at colors random len random 255.255.255 show box-list ] ] -- Carl Read