ASP .net client server refresh issue

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ASP.NET

I am using a checkbox and a checkbox list in one of my web pages.
The details of the UI are,

1) Initial UI
Color --> Header Checkbox
Red -- > Checkboxlist items
Blue
Green
Yellow

2) Complete selection

The entire checkbox list can be selected / unselected on checking header checkbox

3) Partial selection

When a item in the checkbox list is selected, the total number of selections is checked and to indicate a partial selection, the background color of the header check box is changed to a dark grey. This is to achieve something similar to three state checkbox.

AutoPostBack property is set to true for all the controls.

In a client server environment, there is a time delay and if we make two continuous selections in the checkbox list, an update of the header control is done for the first selection and by the time UI is refreshed, the second selection is gone.
I also implemented the above one using JavaScript but then also the behavior is same.
How can it be done in a better way?