About your question on why black is not used even though it provides the highest contrast to white: thats not practically true. The problem is, that black and white have the same hue and color saturation (or rather they have no color saturation, and thus the hue is undefined in both cases), so they only differ in brightness/luminance. And a difference in brightness can easily be caused by different lighting conditions.
So for black-dyed de-icing fluid, you couldn't reliably tell whether a black-looking spot has been de-iced, or if it is just not well lit. Similarly, a white-looking spot may not have been de-iced, or may just accidentally reflect more light that its surroundings (e.g. due to specular highlights, retro reflectors, different incidence angle to the light source, or different surface reflectance), Colored fluids solve that problem, as color (e.g. green dyed liquid vs. white snow) barely changes under varying lighting conditions.