Profile photos are automatically scaled to 604x452px (when viewed at largest), and in the previews to a square format of 50x50px. The format on the main profile page is not a square, it can also be portrait format. But the width is always 200px.
So to prevent facebook to destroy the picture when making a square format from it, it’s best to make it square in original. That is, 452x452px is the recommended original size for profile images. They get then automatically scaled to 200x200px and 50x50px.
You can add a PNG image as profile image, but transparency in it is converted to black. So this is no option to integrate your image better with the facebook design.
To integrate your profile image with the facebook design, use the facebook colors: white (RGB 255,255,255), mid blue border color (RGB 214,221,231) and light flue area color (RGB 239, 239, 247).