TBH … unless the drone’s quite close, the drone is too small to discern a colour. It just remains as a spot against the much brighter grey sky.
Nothing beats strobes for visibility … and there’s more about them here …
- Those CREE Strobes are Sooo Bright!
- Strobe LED's
- or a search on “Strobe” will give you more : Search results for 'strobe in:title order:latest' - Grey Arrows Drone Club UK