I am making a WPF project. While running the application, as I take my cursor to a button, it gets highlighted by blue color filled inside it.
Now, I want to remove
The link isn't working for me, so I can't see exactly what you are getting at, but I assume that you're trying to change that default blue-ish gradient. You need to override the template for the button in a style, and then you can customize it to look however you want. You can't just set the background color or use triggers to change it without overriding the template, because the default template has some extra stuff in it to show that gradient effect.
Here is an example of a button I have used before that is fairly straightforward. This example uses a trigger to change the foreground color of the button when it is pressed, but will never change the background color.
Also, if you're interested, here is what the button's default template is: