The darkish gray dip is mostly avoided by using a linear colorspace. Interpolating in HSV can introduce weird artifacts. Mostly due to H being circular, if you

The darkish gray dip is mostly avoided by using a linear colorspace. Interpolating in HSV can introduce weird artifacts. Mostly due to H being circular, if you naively interpolate between two close shade of red, you might go through all of the colors of the rainbow. Interpolaring in a perceptual colorspace might make sense in certain applications, but if arithmetic on color values is involved then a linear colorspace is a good default (and premultiplied alpha, but that's an other story).