It can be difficult to get a perfect balance between top and bobbin. That's why many quilters just use the same color in both. After laundering, they become less noticeable.
Little Monogram designs? If you have an embroidery machine, some of the colored thread will show on the back.
Any time you ask a question about your machine, you should include the manufacturer and model. Don't have a clue about the "stitch balance adjusting thingy"...