Ok, this is Silver Nitrate in Acetic acid. It tests for retained hypo. It forms a brownish red stain in the presence of hypo and Silver complexes which cannot be seen in red light. The Kodak instructions that I have are not specific to wet or dry. They are vague. They are vague also as to the lighting conditions. I have several sets of documents though so I'll look more.

Anyhow, Silver Nitrate in acid and in excess of that needed to react with a halide will form this color, but the color is not fully evident until exposed to ambient white light. If you leave a well washed print out in the light, and with this test solution on it, the tested area on the print will also darken even if clean, so extended white light can give a false positive! The color from the test solution that is valid shows up within the first 5 minutes or less. It is called "printout".

It is akin to what happens if you put a drop of Silver Nitrate on your finger (not recommended) and expose it to light. Your finger turns dark brownish black.

So, one drop on a white area on a print. Expose to light and over 5 mins if you see a dark brown red stain, the wash is insufficient. If it is good, you see no color or a light yellow. If this "good" print is left in the light for a few minutes to several hours it will turn as dark as a "failed" print test.