Drying times will vary
To follow up on Fat over lean, the drying times for various oil paints will vary according to the amount of oil necessary to properly suspend each individual type of color pigment. This taken into account with the varying reaction of the different colors' pigments, when mixed with an oil medium, will result in different drying rates for each unique color of paint.
From the Winsor & Newton introduction to their artist grade oil color paints:
Fast Drying [around two days]:
Permanent Mauve [manganese], Cobalt Blues, Prussian Blue, Raw Sienna, Umbers, Flake, Foundation and Cremnitz Whites [lead].
Medium drying [around five days]:
Winsor Blues and Greens [phthalocyanines], Burnt Sienna, Cobalt Violet and Greens, Ultramarine Blues, Mars colours [synthetic iron oxides], Sap Green, Permanent Alizarin Crimson, Ochres, Cadmiums, Titanium White, Zinc White, Lamp Black, Ivory Black, Pyrrols, Bismuth Yellow, Perylenes.
Slow drying [more than five days]:
Winsor Yellows and Orange (arylides), Quinacridones, Alizarin Crimson.
Long drying times are very important for oil painting. As oil paint maintains its pliability, corrections can easily be made until it is touch dry. Most oil paints are touch dry within two to twelve days giving the artist plenty of time to create their vision. A typical painting may take 6 months to fully dry. Very thick paint applied using an impasto technique can spend up to 2 years to dry down to the canvas.