Kevin,
Galvanized soffits can leave a rust streak on the siding but it is by no means perminate, you can remove this stain with CLR (Calcium/Lime/Rust) simply apply it to the stain and follow normal washing proceedures and wash from the bottom up. Galvanized steel has not been used on houses since about the early 70's and was mostly found in drip edge and some soffit. Very rare to find since aluminum has been around since the 60's and 70's also.
As for yellow streaks on vinyl siding by using bleach, maybe at household full strength but never diluted. Bigger and better chance that it happened from poor washing habits, spraying water into the weep holes, if that is the case they probably used tar paper to back the vinyl and what you are seeing is tar stains coming out of the weep holes. Hope it helps you understand, but for the bleach, no problem in weeker dilutions.
DD