My ketosis measures around the middle of the scale most of the time but it has at times got darker or lighter. As Upsy-Daisy said, you are in ketosis no matter which shade you measure on the scale, but it just shows you what level of ketones are coming out in your urine. Being really dark purple doesn't mean you're in a "deeper" state of ketosis and burning more fat so don't be concerned about that - but I would agree with the suggestion to increase your water intake as a darker colour does suggest a higher concentration of ketones (you would be a lighter colour if they were a bit more diluted with extra water).