A lot of beginners think a search coil must be black in color. That is not so. A white coil in metal detecting practice is better.
There are a few circuits inside the search coil, their immobility determines total stability and accurate operation of your metal detector. The manufacturer hasn’t got so many means to ensure this immobility (at that, the coil must be light enough). They almost always apply polymer as fixing material. But polymer softens with rising temperature. Which surface warms up faster in summer, during the heat? White or black? So, in the heat a white coil is more reliable.
Have you ever gone hunting for several hours straight? And what is the usual color of the soil under your feet? I have the dark one. And if you have been looking at the black coil passing over the dark soil for several hours, you begin to understand there is lack of contrast to focus your sight.
During long searches a white coil is more comfortable for eyes. You can look after the coil motion pattern easily and without strain.
If the coil is black, however, a color beacon on its body can be of service (the one, for example, Mars MD coils have). Such ‘fishing buoy’ keeps your sight and enables to control the sweep pattern.
If someone wants to say that a white coil becomes more soiled, this is also a misapprehension. The coils get dirty equally. But the clods stuck to the coil surface may give false responses. You should take care of this and clean in time. On coil of what color can you see the soil stuck to it better? Sure enough, on the white one. Happy finds!