All of the Age of Steam map rules I have seen are only the differences between the base AoS rules and the map's rules and, as I mention below, sometimes they are not complete without knowledge of the features of other expansion maps.
I do not know of a unified Age of Steam map rules resource, although depending on the designer the rules may be on BGG or on the designer's web site. At one point I created a fairly comprehensive and up to date list of Age of Steam maps which includes designers, that might be a good place to start.
It is fairly well documented that anything that John Bohrer retains the copyright to (including the base game rules) will not be made available online.
Paris being multicolored is actually the easiest rule to manage on the France map, it just behaves like all of the colors present. The other rules, like engineer being required to build over mountains and the non-existence of bankruptcy are less obvious.
White lines over water almost always indicate a sea route or ferry that can be built as a single track tile build at a fixed cost (which can vary by map). If the line is dotted, it usually means that one or both of the ends of the line are towns that must be urbanized before the link can be purchased.
One of the major challenges of AoS map rules is that they all assume a certain amount of familiarity with the rules of AoS and, in many cases, with the rules of one or more expansions for AoS. For example, the New Zealand print and play map for AoS has sea links with town terminals but it does not spell out when they are allowed to be built. I believe this is due to some sloppy thinking on the part of the designers, as they assume an accretion of knowledge about AoS that may or may not exist for a given gamer or group.