Flour was the course marking standard in Montgomery County Road Runners Club in the 1980's until we got in to trouble with it. I marked flour arrows on a bike path on a humid summer morning. Later that day, a brief rainstorm came through. A week later, I ran through the same area and I saw that the flour arrows were still there. Curious, I stopped to examine one. It had become just wet enough to become a paste but not so wet that it dispersed. That paste then baked on the asphalt path in the summer sun. Months later, the arrows were still there. MCRRC got a complaint from the Park Service about the "paint marks on the path". To the skeptical park manager, we explained that is was baked flour. He said "no more flour". Those baked-on arrows were still visible three years later before finally fading away.
We switched to granulated lime. No one had a problem with that except a sensitive resident of an upscale neighborhood whose street we traversed in a popular race who reported to the police her suspicion that rogue vandals were "painting possibly anti-Semitic symbols on the road". Problem was, it was no better than flour on a windy day, and useless on a rainy day.
Hence the switch to colored tape. After the Pike's Peek 10K on the busy Rt. 355 in Rockville, MD, one year, the one mile split volunteer neglected to pull up the tape across the road. She had no difficulty finding the one mile mark the following year because the tape was still there, intact.