The Atkins Community - the official Atkins site - frowns on ketostix now as a way of measuring ketosis! They say that results are often misleading and that the stix are more likely to indicate the level of dehydation than the level of ketones in the urine.
I don't use them much these days. Indeed I only use them at all because I bought three packs on offer last year!
If they reassure you, fine. However if you are feeling a lessening of appetite and sticking well to your plan you are almost certainly in ketosis. Even the very faintest blush on the stix indicates this. And you can see no colour change at all yet still be very much in ketosis!
Good luck with Atkins!