I think it's important to realize that the ketone test strips are only one tool to measure progress and not a terribly accurate one at that.
Yes, some people feel they need that visual confirmation of the sticks turning color to feel that they are on track but consider that they can also measure alcohol (which is metabolized to ketone bodies) and dietary fat as well as burned body fat before putting too much stock in them or using them as your only tool to gauge the eficacy of your plan. I've seen people literally going to extremes to try to get those strips to turn color even though they were losing weight just fine. I've even seen people quit low carbing because the strips weren't turning color, assuming that the plan wasn't working even though they were losing weight.
Use them as a tool if you need the visual confirmation, but don't panic if they're not the color you think they should be or the color changes from day to day and use other methods of gauging progress as well such as the tape measure and how your clothes are fitting.