This table is adapted from @Montgomerie2006 and lists all spectral descriptors that are computed by the summary function in pavo.

Color variable	Names used	Formula	Reference
Brightness	Total brightness, total reflectance, spectral intensity	\[B_1=B_T=\int_{\lambda_{min}}^{\lambda_{max}} R_i = \sum_{\lambda_{min}}^{\lambda_{max}} R_i\]	@Andersson1999,@Andersson2002,@Ornborg2002,@Andersson1998,@Smiseth2001,@Saks2003,@Pryke2001,@Shawkey2003
	Mean brightness	\[B_2=\frac{\sum_{\lambda_{min}}^{\lambda_{max}} R_i}{n_w}=\frac{B_1}{n_w}\]	@Delhey2003,@Siefferman2005
	Intensity	\[B_3=R_{max}\]	@Andersson1999,@Keyser2000,@Keyser1999
Saturation	Chroma, reflectance ratio, spectral purity	\[S_1= \frac{\sum_{\lambda_a}^{\lambda_b} R_i}{\sum_{\lambda_{min}}^{\lambda_{max}} R_i} = \frac{\sum_{\lambda_a}^{\lambda_b} R_i}{B_1}\]	@Ornborg2002,@Andersson1998,@Smiseth2001,@Siefferman2005,@Peters2004,@Shawkey2003
	Spectral saturation	\[S_2 = \frac{R_{max}}{R_{min}}\]	@Andersson1999
	Chroma	\[S_3 = \frac{\sum_{\lambda_{R_{max}}-50}^{\lambda_{R_{max}}+50} R_i}{B_1}\]	@Shawkey2003
	Spectral purity	\[S_4 = \lvert b\text{max}_{neg}\lvert\]	@Andersson1999
	Chroma	\[S_5=\sqrt{(B_r-B_g)^2+(B_y-B_b)^2}\]	@Saks2003
	Constrast, amplitude	\[S_6 = R_{max} - R_{min}\]	@Keyser2000,@Keyser1999
	Spectral saturation	\[S_7 = \frac{\left(\sum_{\lambda_{320}}^{\lambda_{R_{mid}}} R_i - \sum_{\lambda_{R_{mid}}}^{\lambda_{700}} R_i\right)}{B_1}\]	@Andersson2002,@Pryke2001
	Chroma	\[S_8=\frac{R_{max}-R_{min}}{B_2}\]	@Andersson2002,@Smiseth2001
	Carotenoid chroma	\[S_9=\frac{R_{\lambda_{700}}-R_{\lambda_{450}}}{R_{\lambda_{700}}}\]	@Peters2004
	Peaky chroma	\[S_{10}=\lvert b\text{max}_{neg} \lvert\frac{R_{max}-R_{min}}{B_2}\]	@Ornborg2002
Hue	Hue, peak wavelength, spectral location	\[H_1=\lambda_{R_{max}}\]	@Andersson1999,@Ornborg2002,@Andersson1998,@Delhey2003,@Smiseth2001,@Keyser2000,@Siefferman2005,@Shawkey2003
	Hue	\[H_2 = \lambda_{b\text{max}_{neg}}\]	@Andersson1998,@Smiseth2001
	Hue	\[H_3 = \lambda_{R_{mid}}\]	@Andersson2002,@Smiseth2001,@Pryke2001
	Hue	\[H_4 = \arctan\left(\frac{B_y-B_b}{B_r-B_g}\right)\]	@Saks2003
	Hue	\[H_5 = \lambda_{b\text{max}_{pos}}\]	@Keyser1999

$R_i$: percentage (or proportional) reflectance at the $i$th wavelength
$\lambda_{max}$, $\lambda_{min}$: upper and lower (respectively) limits of wavelengths
$n_w$: number of wavelength intervals used to calculate $B_T$
$R_{max}$, $R_{min}$: maximum and minimum percent reflectances, respectively
$\lambda_{R_{max}}$: wavelength at maximum reflectance
$b\text{max}_{neg}$, $b\text{max}_{pos}$: maximum negative and positive slopes of reflectance curve in a region of interest
$B_r$, $B_y$, $B_g$, $B_b$: total brightness in red ($r=625-700\,nm$), yellow ($y=550-625\,nm$), green ($g=475-550\,nm$) and blue ($b=400-475\,nm$) segments of the spectrum
$\lambda_{R_{mid}}$: wavelength at the reflectance midpoint between $R_{max}$ and $R_{min}$ (i.e., $\frac{R_{max}+R_{min}}{2}$)

References