asp.net and sql server

Kamal, 

Firstly you might want to load the list of colours in the drop-down and then either on auto postback or on some trigger you want to save it back to the database.

You can start from there - 

Loading dropdown lists in ASP.NET - 

http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.dropdownlist(v=vs.110).aspx

Saving data from dropdown list - 

http://www.codeproject.com/Questions/677148/how-to-save-dropdownlist-selected-value-in-datatab

  Are you filling all colorname in dropdownlist at load.