I'm not clear on whether you're trying to limit the selection to a specific date range, or whether you want to disable arbitrary dates within a range.
If it's the former, you should be able to specify minDate and maxDate when initialising datepicker. See here.
If the latter, you should be able to use the beforeShowDay option. There's a nice explanation on this question. The second element of the return value is a class name - using that with some corresponding CSS will allow you to see the colour. You can stop it being selected at all by returning false as the first element of the return value.