收藏被修改;从LIstBox中删除ListItem时，枚举可能不会执行错误

I have two ListBoxes, lstAvailableColors and lstSelectedColors. Between each listbox are two buttons, Add and Remove. When a color or colors is selected in lstAvailableColors and the Add button is clicked, I want to remove them from lstAvailableColors and display them in lstSelectedColors. Also, if colors are selected in lstSelectedColors and the Remove button is clicked, I want to remove the colors from lstSelectedColors and add them back to lstAvailableColors. When I do this, I get the following error when it removes the item:I have two ListBoxes, lstAvailableColors and ls