How do I find the right shade of foundation?
The jaw line method is a good way to do this but, for some, it's not
enough to properly determine the color. As for getting it on the jaw
line, you can use what method (brush, sponge, etc.) you normally
use, just don't do your whole face. Apply near your chin and lower
cheeks to see how it blends with your neck.
If
you don't think that's enough to judge, maybe try a half-face of two
colors to compare. The right color (which you may have to find by
mixing two colors together) will disappear into your skin and make you
look "alive," for lack of a better word. It will blend in with your
neck and overall tones, and you'll look like you're not wearing any
makeup at all.
As for lighting, it's wonderful
if your foundation matches in EVERY situation, but sometimes-direct
sun, a tinted windshield, fluorescent lights, etc., can throw off the
look. If it matches 95% of the time, and people start telling you how
great you look (new haircut? back from a vacation? etc. LOL!) then you
know you've found your color. :) If you're a cool girl, you have
options. You can wear a cool-toned foundation to match your face/neck,
or wear a more neutral or yellow-based foundation to counter any
redness, yet still blend in.