There is no one answer to this question, as it primarily depends on where the net is going to be used. In outdoor areas, darker nets are less noticeable than light-colored ones, as they contrast less with the background. Conversely, from a certain distance a light-colored net can appear like a wall, due to the heightened contrast. The same is true for the view to the outside (e.g. cat nets on the balcony). However, if the net is to be mounted directly in front of a white wall, white would obviously be the best choice.
In the case of thicker safety nets in indoor areas (e.g. staircase nets or loft bed nets), the color does not affect the visibility of the net. Here, you should base your decision on the colors of the surrounding area or on personal taste.