I just bought a Fluid "S" on ebay. I know what shade I wear in the water-in fluid foundation, but wasn't sure how that would translate to the "S" line. ** Color wasn't a match for my skin, I bought one of the darker colors and it's still too fair for my fair/med skin. That said, this would be a great product if I were to find the right color. Now that it's winter, I like the water-in fluid better for my dry skin. I second reviewer who said it's like liquid skin: your skin, only even-toned and smooth--Calomine lotion smell notwithstanding.
I asked Shu for color guidance and rec'd this answer:<p>
All Foundation shades are comparable to each other and range from 300 to 900 on a scale of yellow to red hues. Depending upon your desired effect, you would choose either a match of your skin tone, or a shade more red or yellow to achieve the desired complexion.
300’s have a red/pink undertone, 700’s have a slight yellow base, and 900’s have the most yellow undertone. 500’s are the neutral family.
The next number values refer to the light to dark factor. The higher the number, the lighter the shade in the YR range and vice versa.