Change Label color according to Numbers of days from date c#

I have a team working together 30 days and I have a textbox insert into date if you insert 01/01/2016(TextBox1) automatically display in autoPostBack 10/02/2016 (TextBox2)

I want if the team working together from 1-27 days the color of label change into green and from 28-29 days change color into yellow and more than 30 days the label color change into red.