An officer should never assume that a realistic looking item is not real if it is colored, so requiring non-guns to be colored is silly.
Someone painted this Cobra FS 380 for unknown purposes. The police claim that it was to make it appear to be a toy, but people have been customizing and adorning the appearance of weapons for centuries. From fox19.com:
CINCINNATI, OH (FOX19) –
Orlando Lowery was in court this weekend for allegedly painting his .380 caliber semi-automatic handgun to look like a toy.
It is only in recent times that firearms could easily be made in many different colors. As the capability to do so has emerged, more and more people are taking advantage of it. Here are some pistols in different colors.
This Pink Glock is fully functional. One advantage of brightly colored handguns is that they are highly visible. It is hard for a gun to be a credible deterrent if it cannot be seen. I have read of more than one incident where a person armed with a mini-revolver was forced to fire it to prove that it was real.