Maybe a Tension Problem?
 

I have 100% cotton 50/2 Aurifil thread, red in top, white in bobbin. On the backing, I am getting red dots showing thru from the top. What needs to be adjusted? TIA

Try making the top tension a little tighter.

The top thread (red) is being pulled into the backing, so that means that your bobbin tension is stronger than your top thread tension, and you need to get them balanced. Start by tightening up your top thread tension - try tightening a half unit at a time and then stitch a test (on a quilt sandwich) and see how it looks. If you can't fix it with just the top tension, you can then try loosening the bobbin tension. On some machines, this is done by loosening a screw on the bobbin case. Check your manual for your sewing machine.

Many experienced quilters recommend always matching the color of the top and bobbin thread to avoid this problem. Some note that even if things look good at first, after a bit of time, the annoying dots of color can show up (when you stitch with two different colors of thread). They recommend picking a thread color that is good for your quilt top, and then picking a backing that you like with your thread choice.

I always try to pick a thread that can get lost in my patterned backing. Avoids all kinds of problems :)

Agree w recommendations stated and double check top threading is correct and that u have a new needle
I was experiencing the same and as it turned out my top machine threading was off.