I too believe in this
film colors thing.
You see, the output from a digital camera is a flat reproduction of the RGB triplet hitting the sensor, thus they seem to lack "life". In film, each color exhibits a different response curve, varying with film brand, ASA/ISO
and lightning condition, further producing results distinct enough to be recognizable. That's why we can say
"I love that Kodachrome skin" or
"Nice Velvia sky", because the inherent
quirkinesses of each film imprint some character to the output.
I got the specsheets for some films (Velvia, Provia, Kodachrome) and some sample images, and I'm slowly building a library of presets for Aperture for applying the same response curves those films capture. It's not 100% because film and sensor respond different to light (sensors will always output all colors equally for a set ISO, while film is not linear), so the digital image you have when you apply the preset is already different than what film would have captured. Color reversal and slides also behave differently (slides retain dynamic range and don't lose detail on high contrast areas as happens with print). Trying to reproduce some of those nuances is hard, specially with compressed data formats and low dynamic range output media like a computer screen, thus the result is never 100% like seeing a slide on a projector. But tweaking the response curves can get you long a distance.
Some of the results so far:
Original
The flat-and-boring original.
Kodachrome 64
Kodachrome normally responds with warm mid/highlights, soft darks and good contrast
Velvia 50
Saturated blue highlights, greenish darks, contrasty
Provia 100
Red/purple casts, saturated colors, retains more detail on dark areas
I compared those to the reference photos I got and ended very happy with the results. For high ISO film is harder because matching the grain is not trivial, but I'm studying how to do that also.