Font colors

If I click ctl-f a search box opens up. The text color is black and background color is white, (easy to read).

But if I highlite the text or come back to it later, the text is white and the background is dark blue, (hard to read).

How can I change background color.

As I remember, it has something to do with left clicking on the desktop and making a square. And changing the color of that square.

Don Cole