Shell spectral representation of two spectral lines at opposite edges of the visible spectral range. Left: two spectral lines in the $(f_0,\frac{\mathrm{d}{f}_0}{\mathrm{d}\lambda })$ shell space. Line 4203.9790 Å at the blue part of the spectrum has the larger loop than Line 6496.9079 Å at the red part of the spectrum in $(f_0,\frac{\mathrm{d}{f}_0}{\mathrm{d}\lambda })$ space. Right: line 4203.9790 Å and 6496.9079 Å in the $(f_0,\frac{\mathrm{d}{f}_0}{\mathrm{d}v})$ shell space. The line in the blue part of the spectrum follow the same loop as the line in the red part when considering the common normalized flux, from 0.9 to 0.4. Therefore, the chromatic effect due to dispersion is suppresed in the $(f_0,\frac{\mathrm{d}{f}_0}{\mathrm{d}v})$ shell space.