If you are looking for the right color, you can completely customize the text color for your thumbnail and the banner very easily, check it out!
To change the color of the font and the banner click on Edit Styles at the bottom:
Below Text Overlay, you will find the Text Color and the Banner Background Color options.
In this example, you can see a green banner with white text on it.
There are many things you can do, even removing the banner and simply leaving the text over your video.