(too long for a comment)

    Plot[{ColorData["VisibleSpectrum"][x][[1]],
          ColorData["VisibleSpectrum"][x][[2]],
          ColorData["VisibleSpectrum"][x][[3]]}, {x, 380, 750}, PlotStyle -> {Red, Green, Blue}]

![RGB components of visible spectrum][1]

It doesn't seem that you'll be able to obtain `Yellow` (`RGBColor[1, 1, 0]`) from `ColorData["VisibleSpectrum"]`; unfortunately, the docs say nothing about how they're blending the colors to produce `"VisibleSpectrum"`.

  [1]: https://i.sstatic.net/RNdnb.png