2 blue lights traveling low below cloud cover along I-35On Thursday night, January 29th, 2015, shortly after dark, maybe 7-8PM, my daughter was on her way home from Waco, towards Austin, on I-35. Somewhere near Salado, she observed 2 blue lights traveling southbound near her. They appeared to resemble aircraft landing lights, but were a deep blue (not the blueish tint of some LED lights, blue like emergency lights). One was solid and one was blinking slowly. They appeared to be on the same craft. She observed it until about Jarrell (roughly 8 miles/5 minutes), and lost sight of it, as it continued south. No aerial maneuvers, just a steady flight. The coloring was the strange part. Also, there was a "low ceiling" so no stars were visible. It was flying below the ceiling of clouds, maybe 2000-3000 feet? I know of no aircraft that uses blue lights such as this. No other colors were seen, no strobes, just the 2 blue lights.