The AMBRE templates have two models, plane-parallel (p) and spherical (s) geometries. In the p-model, we have four parameters: effective temperature (Teff) and log-gravity (logg), stellar metallicity ([Fe/H]), and alpha elements ([alpha/Fe]).
 
In the gri diagrams (HSCColorsSelection_W02_p_*png), the synthetic HSC colors of the p-models with Teff=6000 - 7300 K (equivalent to F-stars) are plotted.  The black dots are HSC stellar objects fetched from PIPE2D-382.  The "crude" color criteria to select F stars is defined by the green box, which is drawn by hand. The selection criteria enclose almost all the models. 
 
The selection lines pass through (g-r, r-i) = (0.06, -0.11), (0.41, 0.07), (0.02, -0.06), and (0.30, 0.13). Thus, the criteria are described as
r-i > 0.514 * g-r - 0.141
r-i < 0.679 * g-r - 0.074
r-i > -1.25 * g-r - 0.0350
r-i < -0.545 * g-r + 0.294
 
The parameter dependences of synthetic HSC colors are shown in color-color diagrams. The sequence of red-blue is formed by Teff, primarily. This sequence is magnified by log g at a fix Teff. The dispersion in a perpendicular direction to the red-blue sequence is made by stellar metallicity. [alpha/Fe] has a small effect on the colors.
 
In the s-model case (HSCColorsSelection_W02_s_Teff.png), the synthetic colors are shifted to bluer than the p-model. We need to consider how to handle these two models.
 
 

The crude selection criteria is provided. This ticket is closed. The issue on the difference of the atmosphere models (parallel and sphere) will be studied in other tickets in the future.