May have worded this poorly, but when you look at the color spectrum, it appears (to me, my thinking may be flawed) to be the primary colors red, yellow, and blue and their intermediates. Red to yellow with orange in the middle, yellow to blue with green in the middle, and blue to what would be red, with purple in the middle. Except there is no red at the end of the natural spectrum, just at the beginning. So is it just a nice coincidence that it wraps around perfectly?
In: Physics
It’s not necessarily a coincidence. It’s directly implied by the fact that we perceive the full spectrum as white/colorless/neutral. Let me try and summarize the argument:
Basically, the brain interprets as “neutral” things that reflect the entire spectrum. Because our eyes has three types of receptors, this (simplified) physically translates to “all three receptors are receiving roughly balanced signals”. Given that this particular balance remains “neutral” no matter the total brightness of the signal, that leaves only two dimensions for color information. In other words, our perception of color will form *some* two-dimensional space centered on white.
I recommend taking a moment to look at [an actual graph of this two-dimensional space](https://upload.wikimedia.org/wikipedia/commons/3/3b/CIE1931xy_blank.svg), though the following argument does not assume any specifics about it.
I will gloss over the non-ELI5 topological details, basically what it boils down to is that this 2D spectrum of colors can essentially be further broken down into “colorfulness” and “hue” components, in a way that necessarily follows from the fact that “white” is in the middle. “Colorfulness” is basically “the distance from neutral”, i.e. the closer you get towards white, the more things will tend to fade or “lose their color”.
So if we have one axis for brightness (independent of color), one axis for “colorfulness” (distance from white), that only leaves one axis left for the actual *color* (i.e. what you describe as “the spectrum”). And because we already know that white is in the neutral / center position, this remaining axis must, in some sense, “loop around” white, such that you can make a full round trip through all colors without ever going through white.
**tl;dr** it would be mathematically impossible to have a “disconnect” in the color wheel without also destroying the property that a balanced spectrum is perceived as white/neutral.
p.s. in color science, what I called “colorfulness” is usually called either *saturation* or *chromaticity*, what I called “brightness” is often called *luminance* or *lightness*, and what I called “color” is usually called *hue*.
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