***Comparing good and evil to the electromagnetic spectrum is a flawed comparison. With "red," we have a standard of measurement to decide what qualifies that color, but we have no such unit with morality. Until our technology becomes about 100 times more advanced and we can say "if a certain action stimulates these two million neurons, the subject views the action as evil," the best we can hope to do is ask someone "Do you think this is evil or not?"***
For example, the standard of measurement to decide color breaks down when we get to the picometer scale. On the other hand, if we talk in terms of more general nanometer scales, there is much more agreement on the color scales.
Similarly, the standard of measurement to decide correct moral action breaks down when we get more specific on the boundaries. On the other hand, if you generally ask if it is okay to harm people at random, I think the general opinion in the world is that this is a wrong action.
Both of these examples are the same issue. We are taking human concepts (e.g., color and morality) and setting standards that define one color from another and one morality from another. The standards that arise from these arbitrary agreements can easily be compromised by scaling (e.g., moving from the nanometer scale to the picometer scale).
The fact of the matter is that there really is no such objective standard as to what is 'red' and what is 'evil'. There are simply useful descriptions that are convenient to categorize both abstract and tangible concepts.
The more we scale, the more abstract our concepts become. We can decide to avoid defining abstract concepts, but even that rule would need some form of cutoff that would vary upon circumstances. For example, I heard the Eskimos have many more classifications for snow then us below the Arctic Circle. For Eskimos the classification of various kinds of snow isn't as abstract as it is for us.
What dictates our interest in defining abstract concepts is the advantages we obtain in doing so. By defining red we can tell someone what color we like without having to show them. But, if you are a painter this might not be specific enough. So, you need to tell someone else that what you really like is 'cottage red'. This holds a more abstract meaning, but if everyone knows what you mean by 'cottage red' this tells you more of someone's thoughts than if they just said 'red'.
Similarly, by understanding what someone means by evil can be very helpful. This is how standards are realized. The word gets out that someone is using a certain definition to mean a certain description. This is when words as symbols take on their value in language.
Warm regards, Harv