hi, i'm reading my friend's friends and i do lots of knitting (but i can't spell, sorry). Do you know the yardage (length of yarn per ball, it doesn't have to be in yards that's just the word for it) of the like pattern sepcified yarn and the yarn you are using?Becos then you could work you how much purple to get. If you don't then after you've used one ball (well 2 balls, one of each colour becos it's entrelac) you could measure the area you've knited and compair that to the total area you want to make to get an idea of how many balls you'll need.
But obviuosly you can't acatully have too much purple.