Yes, check tension when changing colors of thread by sewing a bit on a scrap sandwich....I make my own w/ muslin,batt,muslin and serge around edges....I always check stitches when changing thread color...and yes, dark colors are more prone to cause a tension change(top).....but needless to say a nano-speck of LINT can really be the cause of so many messes!!!!!! I clean bobbin and bobbin area with each bobbin change or thread change......