Try some subtle blonde highlights around the perimiter and the top, as well as the hairline - it usually solves this blending problem and distracts the eye away from the blend (if you do the highlights right, it's hard to pick out where the piece hair ends). Try it, you will be amazed with the results! Get a cheap blonde highlighter kit and follow instructions in it. Don't use too much bleach or leave it too long or you will end up looking like a 20 year old kid