Hi,
When i select a cell to edit a yellow border is appearing i want to change that yellow to blue, i tried to change it in GridViewCell template, but not able to see any related elements.
You can predefine the styles for the TextBox based on the current theme that you are using. You have to locate the file - "System.Windows.xaml" and add it to your project. Then find the styles for the TextBox and change the colours of "MouseOver" and "Focused" visual states. For your convenience I have attached sample project.