If something as blatant as the color green can be said to not exist isn't conceivable that nothing exists?

To begin with, why should we think that colors do notexist? Many philosophers have arguedthat colors are secondary properties ,that is, they are properties that are perceived, and as such properly exist inthe perceiving mind rather than external objects. But many of those philosophersalso think that there are primary qualities which external objects haveindependently of the mind, and which, together with the perceiver, areresponsible for the perceived secondary qualities. On that view, colors exist, they just are not“in” external objects. Some philosophers, such as Berkeley,deny the existence of the material world, but maintain that colors and other “sensiblequalities” are real perceptions in the mind. But aside from the question of thereality of color, the question of whether total non-existence is conceivable isan important (and related) philosophical question. I recommend Descartes’ Meditations on First Philosophy as a starting point.

I have always thought that with the primary colors and black and white, you can create any color that we see. This may sound dumb, but then how do you make neon colors? What else can you add other than the previously mentioned colors (or lack of)?

Neon red is simply red light emittedfrom an enclosed clear transparent vacuum tube containing the element neon, towhich an electrical current is applied. Neon actually emits a red-orange color.Other colors can be obtained by introducing other gases in the enclosure andalso by changing the color of the tube. What you may be asking about is thedistinctive glow emitted from a neon tube. The red of a neon tubeappears different from the red of a painted surface, for example. Differentmaterials emit or reflect red light in different ways, and our visual system issensitive to many of those differences.