Actually, when Atkins talks about the ketostix turning Lavender or Purple he means that the sticks have various SHADES of lavender or purple.

At least that's what I understand it to mean. Hence you may only get a trace or purple all the way up to the dark purple.

You have to remember that you will go in and out of ketosis throughout the day, because you have eaten way too many carbs, you are drinking a high volume of water and/or depending on your TOM cycle.

I have to admit, I like seeing the ketostix turn colour because it give a psychological boost that something/anything is happening. However, you will find that with time it isn't as important as long as you are losing weight. I often go days w/o checking the stix but I do like to check in now and again especially if I am getting a bit frustrated that things are not happening as fast as I would like.