"Yellow paper" refers to abilities requested by a specific player and sanctioned by the GSM. Although some variant of this mechanism exists in many LARPs, it is common for the abilities involved to only be available to the player requesting them.
In the Steampunk LARP, we invite players to propose new ability ideas for their characters. Such applications should be made to the GSM and will initially be costed for the specific character involved. Successful applications will be added (in unskinned form) to the public list of purchasable abilities, although in some cases the GSM may elect to delay publication of an ability until its impact on the game has been assessed.