Threshold is the mechanic used in The Resource System for Hex, that links particular cards to particular types of magic those cards represent. Threshold is obtained through playing Resource Cards that represent one of the different magics, Wild, Blood, Ruby, Diamond, or Sapphire. To play a card you must not only have the amount of Resource Points the card costs, you must also have met the Threshold requirement of the card. That requirement is shown in the upper left of the card as small colored dots below the Resource Point cost of the card. Cards will have 1 or more dots of a single, or multiple colors corresponding to its required cost. For example:
Cards can be categorized into groups based on their Threshold costs:
There likely will also be cards that contain multiple Threshold magics in their costs.