I see two ways to solve your problem :
UserControl
Your comboboxes seem to always have a colorpicker associated to them, so you should create a custom user control in XAML with just a colorpicker and the combobox. Then you'll be able to work with it as if it was a classic WPF control.
StackPanel
You can instanciate a new StackPanel (Orientation horizontal) for every iteration and add the combobox + colorpicker to its Children elements.