Hamuchi,
You are exactly right about the trace amounts of haircolor, BUT! The oxidation rule is the same with hair dye as it is with fabric dye. After 48 hours, it isn't active any more. The chances of a spot of fresh color touching you in the morning will be smaller than in the evening, when more color has been completed. Dark clothes can have analine dyes, as can hair colors, that may have dried and can be re-activated when wet. These would be something that could cause a reaction. (ever had a T-shirt get wet and "run"?) It is hard to trouble shoot from afar, after the fact.
When choosing a salon, just use common sense and look around. dark dyes leave stains, and you can tell if a salon is clean looking. if it looks like there are color stains all over, then re-schedule your appointment, and then cancel it over the phone later on.
This is why I use separate tools. (Gloves are also a must, and should be removed and kept clean!) The salon I work in is all white, so there is no hiding any color stains. I also always use a towel on every one's neck, as to keep the capes from skin. Things to watch for...I realize I am a minority. =/
G
