Correct. Initially, Newton didn't have indigo in his list for the visible spectrum, but he wanted seven colors instead of six because it matched up with the number of notes in music (and because he liked the number). So at some point there was discussion of removing indigo entirely because it's kinda just a shade between blue and violet that the human eye just isn't as good at distinguishing compared to the other colors. But the neat thing is that what people back in Newton's time called blue and indigo is more akin to what we today call cyan and blue (they know this by looking at his labeled drawings of the light scattered by prisims). Now the spectral colors are: red, orange, yellow, green, cyan, blue, and violet.