I am showing a fixed horizontal progress line at the very top of may Web page that is as long as the viewport width. It is displayed when an HTTP request is pending.

It is similar to the Indeterminate linear progress indicator of the Material Design

My accent / theme color is blue. And the progress line is also blue as you see in the picture. A few buttons, and the header in one of the page, and the footer have also blue background.

What color should I use for the horizontal progress line?

Does it matter that it should not have the theme color as its background?

Update

This is a web page that displays articles (texts). All of the pages has white background and black foreground (text color).

I have only two buttons. One of them is blue and the other one is green. And a header in one of the pages, and the footer have also blue background.

These are the colors that I have used or may use.