Whats happening when switching themes in Sugar CRM or similar kind of application

Can anyone tell me what's happening when i click on a different color / Them icon in sugar CRM or new ORKUT. I am trying to develop a similar kind of application(in ASP.NET) where i need to switch to differ开发者_Go百科ent themes. I dont want to use the ASP.NET SKINS.It seems that there is no page post backs happening when we change the skins in sugar crm /new orkut. Where the changes are being stored ? Do i need to maintain different css for different themes

It looks like the CSS styles for various classes are dynamically changed. You can verify this in Firebug by inspecting a particular element, looking at for instance its background color, then switching the theme. You'll see the background color (or whatever) change. The data for all themes is likely sent down in the initial page render.