The options for Starter Decks are Amethyst and Amber, Emerald and Ruby, or Sapphire and Steel
The ability to split when you pay the costs allows you to use it more as a way to usefully spend your mana than anything else
However, you will see this symbol on MTG Arena while sorting through your collection
(The same is true for card types that don't appear in most games, like plane or scheme.) You can't choose a subtype, such as creature types like Spider or Hero, artifact types like Treasure or Food, or enchantment types like Aura
This isnt an unreasonable speculation considering Final Fantasys deep Japanese ties
When Its Time to Embrace Land Destruction Its clear that from Wizards current understanding and application of the color pie that feels bad effects are something they are hesitant to print