how to identify Clicked buttons

Question

Hai, Iam doing online booking project in ASP.Net by using C#.Net.I have a problem.That is There are 50 buttons and a submit button.When we click submit Button.we have to find which buttons are clicked in That 50 buttons and change the back color of that buttons. I have tried putting them in an arraylist but iam didn't get.So any body give an idea.