Welcome:). You need to post some more information. What is the MID of the discs you are using? What is the attempted burn speed? Have you defragged your source HDD? Is there an error log? Just save as a .txt file, and attach to post using the 'manage attachments' button in the 'go advanced' reply window. Can you also post a Nero Infotool output. Run the tool, then click the diskette icon in the infotool toolbar and save as a .txt file, making sure all 8 boxes are checked. Attach as above.
Visible rings of different shades are common as a burner writes to a DVD at different speeds and recalibrates its laser power. It is unusual for that to happen to a CD tho.