Because Dominaria could have been any color, we let the mechanics dictate its color
Creatures and spells have been creating and removing them since the games inception, and their uses stretch far beyond mere combat damage
Fear of the Dark Four generic, one black enchantment creature Nightmare 5/5 Common Whenever Fear of the Dark attacks, if defending player controls no Glimmer creatures, it gains menace and deathtouch until end of turn
Naturally, players can build on and modify the Starter Decks as they collect more cards, or use their new knowledge to make a new deck from scratch using some of the cards in the Starter Decks
After the Eldrazi Emrakrul twisted them, they became the herald of nightmares
once you know the value, your goal is to maintain the condition of the card over time by keeping it safe from forces that will degrade the card and its value(light, heat, humidity, water, the enemies)