After fasting for 3 & 4 days, I barely turned the strips any colors (with a blood reading in the 4+). I have had them turn pretty dark randomly just eating keto but I have no idea what logic the kidney is using.
I would take “trace” ketones as a positive and use them that way.
I am using a Ketonix which has shown me to be in Keto increasing each day. The strips I have show negative, I prefer to put my faith in the Ketonix.
Urine strips only work for brand new keto participants in the few weeks. After that they become unreliable and give inaccurate results.
Get a blood meter. I use keto-mojo, which is a good one.
You’re absolutely fine. Strips only show excess ketones excreted in your urine. Don’t get nutty about ketone levels, you’re clearly in lipolysis, losing fat, and being successful. Lipolysis drives ketosis, ketosis doesn’t drive lipolysis.
Not really. You cannot generalize. I’ve been seeing dark purple on the pee strips even after a year of strict ketosis.
You can try a Cheap Breathalyzer I think it would work better for your purpose 
“May the Force (fat adaption) be with you”
IF/EF Keto WOE is Self-Discovery 
Good luck and much success in your journey in IF/EF Keto WOE 
Interesting because when I fast that is when my urine ketones are the most positive (to date - only been at this since August 2017). I don’t put too much mind onto the color of the stick (vs how I feel) but I do get curious and test periodically just to see what is happening. We certainly are curious biological creatures how we respond similarly - but not quite the same. 
Keep in mind that ketone levels are highest late at night, and, blood ketone levels may not be reflected in urinalysis.
I usually hit the hay around midnight/1am and every few weeks when I re-check with ketostix it’s purple - but earlier in the day it shows barely anything.
This is different for different people. Mine are highest around the middle of the day and lowest in the evening.
”…For the avid keto folks who have been on the diet for a while, you may be using the ketone blood meter instead. Your testing time, as noted above, depends on why you’re testing. Testing while fasted can be a great way to determine your baseline ketone levels. However, you may find it interesting to see how your body adapts to different foods or even after training. For this reason, testing blood ketones can be done throughout the day to provide a nice snapshot of what is currently going on in your body! Keep in mind, however that movement and exercise can drastically change the dynamics of ketone readings and thus may show differences in levels even with just a mild walk around the house. …” https://ketogenic.com/overview/testing-ketones/
”… A single avocado can have enough carbs to kick some people out of ketosis. The key word here is “some” people…” http://www.dranthonygustin.com/top-10-ketosis-mistakes-prevent/
Those could be inaccurate too. False negatives and false positives happen once you’re keto adapted. If you care about accuracy, a blood meter is the best way to go.
And quite often the darkest colours are caused by dehydration, especially if testing early morning.
I’ve been testing in parallel - urine and blood - and, for me, they correlate reasonably well.
Pee strips never worked for me, even though I can get rancid acetone breath. If you feel good and not hungry there’s your proof that the diet is working.
I like this gals approach and logic!
Being Fat Adapted Versus “In Ketosis”
Keto strips are pretty worthless. That being said, too much and/or certain types of protein can suppress urine spillage. Mine have read negative once I was past 8 weeks, even when my blood ketones register 1.5 - 2.0.
Interesting! Blood levels vs. urinalysis and circadian rhythms is a big subject indeed.
That’s interesting - I bet you are super efficient at using ketones then! Or, like @Msims says:
Also, this…
I’m the same. I get dark purple when I fast.
I’ve been doing the same and see a very strong correlation as well.
I’m wondering if I’m just super inefficient at using them. I find that when I’m maintaining LIGHT ketosis (.04-.08 ish), I don’t show color on the strips, which I’m guessing means I’m using them efficiently. BUT, when I do extended fasting or intermittent fasting in combination with working out, I must be spilling boatloads because my strips get super dark (and my blood measures very high as well).
For me, getting decent color on the strips means that I’m in deeper ketosis, so I like seeing it because I know I can’t knock myself out as easily. Also, I like using the strips because they’re cheaper. Then, if the strips don’t show color, I’ll test with the blood meter to see what’s really going on.
An example: I did a 3 day fast last week and then went skiing all weekend and feasted. I used the strips to keep checking - and miraculously, even with a couple glasses of wine each night, I was still getting color on the strips, because I was basically working out all day and intermittent fasting. However, I came home the day after and even though I ate keto, something I ate must have been wonky because the sticks went white. So, to see what was up, I checked my blood and lo and behold - I was only at 0.2.
My point is, the sticks aren’t accurate at telling you when you aren’t in ketosis, but I would say they’re a cheap way to tell when you are in deep ketosis.
I know a LOT of people say you should just “feel” it, but I’ve never been able to tell when I am or when I’m not without testing. I don’t feel any different, even after 10 months of keto.