Researchers at Helsinki University compared how effectively various colours and patterns on simulated wind turbine blades discourage a tit from pecking a target it has been trained to associate with food. They found that white blades were the least deterring, followed by red-striped blades, one blade painted black, and the most effective deterrent was a combination of black, red and yellow - colours used by multiple species to indicate bad taste or poison. Field experiments with actual wind turbines are recommended, but not yet possible becuse aviation law requires white blades.
Direct link to PDF, summary in Finnish, main content in English.
Finnish-language news article with video of experimental conditions.
Curious as to why aviation law requires white blades
I have no idea of the base reason, but I think it could be something like:
…but since every decent wind turbine has signal lights too, I think it’s mostly bureaucratic inertia that prevents making exceptions. One could always file a permanent NOTAM above an experimental wind generator, telling pilots “here is a wind generator of non-standard colors” and I think it would be OK.