Why isn't there a seam on the color wheel?

One might expect to find it somewhere between red and violet. If the visible spectrum is measured as decreasing wavelengths of electromagnetic radiation, from red (620-750 nm) to violet (380-450 nm), from the lowest frequencies to the highest, placing red and violet at opposing "edges" of this spectrum, why aren't red and violet qualitatively more dissimilar? Instead of this dissimilarity, one finds the same continuity between red and violet that one finds between any other adjacent areas on the color wheel.

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