the white border: join with sl st anywhere on outside edge, do sc's all around and join with sl st to starting ch. in corners, crochet 3 sc's.
did not turn out particularly neat, hope you'll have more patience with the edging.
for more stripy satisfaction, here are some tips from Lucy for joining in a new color and for working in ends as you go (from the 4th picture onwards).
have fun, and since it's become a blog, feel free to send some feedback.