The texture is based on a Gaussian distribution spectrum (wavelength 0 -> 1, width 0 -> 1 and power 0 -> 1). The wavelength is used to set the center of the spectrum and the width is used to set how wide the curve is. The narrower the width, the more pure and saturated the colour.
Octane actually converts classic RGB colours to Spectrum colors. The Gaussian Spectrum Texture eliminates the need for this conversion since is it already Spectrum-based. Spectrum-based color provides better results compared to RGB nodes, this is evident in Texture emission.