This is an entry into a small series of elaborations that include clarifications not given directly on the main page of the game in response to questions people have had about the ruling and the reasonings behind them.

The rule states:

New assets may be worked on prior to the Jam's start time to a 'concept' state.  Colorless sketches, stand alone color palettes, written outlines, visual or audio motifs and such may be established prior to the jam.  Third Party resources are exempt from this rule as long as they are also available for usage/purchase by other participants.  

The intent:

Create a fair playing field for people who knew about the jam prior to beginning and people who discovered it the same day the jam begins, and to enable solo developers to purchase outside assistance in a fair and reasonable way.

Elaborations based on prior questions:

1: New Assets may be worked on prior to the Jam's start time to a concept state.

We define assets here as content that is made to be included in the game or the game's promotional material.  In the game, this would include things such as sprites, backgrounds, cgs, and other content consumed by the player in a regular session of play.   In the game's promotional material, this would include things like capsule graphics, logos, poster/box graphics, or any material that a potential player may consume as part of making their decision to purchase a game that would ordinarily be visible on a digital storefront or game box.

2: Colorless sketches, stand alone color palettes, written outlines, visual or audio motifs and such may be established prior to the jam.

These limits are put into place to create a hard line of how far we allow specific types of assets to be created ahead of time. 

3: Third Party resources are exempt from this rule as long as they are also available for usage/purchase by other participants.  

This part of the rule exists to allow developers to use premade content when they lack the team or experience to create certain content by themselves.  Assets such as these must be available to the public, viewable and purchasable from a public source at the time the jam begins.