Hydrogen-deficient synthetic spectra between 5800 and 6400 Å for four different nitrogen abundances (7.0 ≤ [N] ≤ 9.4 dex) and four different T_effs (4000 to 7000 K). The spectra are normalised to unity. The intensity scales extend between 0 and 1 for all spectra except the ones with a T_eff of 7000 K whose intensity scales are between 0.9 and 1. Cyan represents the CN band-head features, black represents the C₂ bands, and blue is the sum of both. The abundances used for the models are those of a classical RCB star, i.e. [H] = 7.5, [He] = 11.5, [C] = 9.0 and [O] = 8.8, and the C/N ratio increased (∼0.4, ∼3.0, 10, and 100) by decreasing the nitrogen abundances.