Magic the Gathering invented trading card games, and with it, resource systems for trading card games. Countless games following MTG have mimicked MTG’s 5-color mana system, because of course they did, why wouldn’t they?
In Magic The Gathering, spells and creatures cost “Mana”, a resource that regenerates every turn, and builds up over time as you play “land” cards from your hand. Mana comes in 5 colors, Green, Red Blue, White, and Black. Each of these colors has a mechanical identity associated with it, called a “Color Identity”. Mana is the primary thing that divides the design space in Magic The Gathering, to create different types of decks. Of course, there are other things, like card types, and creature types, which have effects that reference one another to create synergies. And there are more broadly playstyles, like Aggro (try to kill the opponent before they can get their good monsters out or reach their win condition), Control/mid-range (shut down aggro and deny key combo-pieces), and Combo (try to stall out to assemble exodia in your hand, then win the game instantly or near-instantly).
Mono-color decks focus entirely on a single type of mana, and usually only play a single “basic” land color. This gives them incredible consistency, because their mana supply goes up every time they play a land, but limits what they have access to in the broader card pool. A mono-color deck may lack “answers” to certain types of “threats” generated by other decks, such as red and black having a tough time getting rid of enchantment cards.
Decks can “splash” cards of other colors into their deck than their primary color, but they’re going to need lands to pay for those cards. You can mix 2 colors of basic land into your deck, but you might end up drawing entirely one color, or entirely the other color, and being locked out of half your spells. This is where Dual Lands come in. Dual lands can generate mana of two different colors, but have a drawback of some kind, such as damaging you, or having some type of blow to consistency, such as entering “tapped”, meaning you can’t use them the turn you play them, which means your mana supply will increase more slowly than an opponent who is playing mono-color basic lands, or you’ll be paying a price in life to ramp at the same speed as your opponent. There are tri-color lands as well, with their own drawbacks.
This means that the decision to run a deck with more than 1 color has a lot of decisions going into how to build your mana-base, but otherwise has a natural mechanical trade-off that is baked into the design of the game, provided that WOTC doesn’t do something stupid, like print dual/tri lands with no drawbacks, or allow you to turn one color of mana into another for too low a price. Each color of mana added to a deck comes with a consistency hit, and makes it that much harder to access spells with a high colored mana cost.
The design of this resource system feeds into the design of card costs. Cards can cost either colored mana, or uncolored mana, or a combination of both. This means that cards can be priced relative to how far you are into the game, and they can be priced relative to how invested you are into a particular color or set of colors.
This card costs a single red mana, and a single black mana, for 2 “converted mana cost” total. This means it can be played fairly early in the game, but only by decks that invest in both red and black.
For comparison, this card also costs 2 mana, but it has no colored mana requirement, which means it’s a staple that every deck can play.
This card can be played by any deck with even a small investment into blue mana, but not by any deck without an investment into blue mana.
And this card can only be played by a deck with a heavy investment in green mana, and usually green only.
By designing the resource and cost systems together this way, it means that decks can reward players for investing heavily into a single color, that they can penalize players slightly for splashing into multiple colors without overly punishing them, and that they can specifically reward investment into multiple colors. And they accomplish all of this while keeping spells costed appropriately to their approximate power level, creating a natural ramp up over the course of a game.
Of course the magic designers have messed this up any number of times, which is why a lot of lands aren’t legal anymore, and a lot of creatures have been banned or made illegal. Currently in the Standard format there’s the issue that Black-Red and Black-Red-Blue simply have access to too good a card pool, because all 3 have very strong low-cost splashable staples.
For contrast, a lot of other games that borrow Magic’s mana system, but not its colors, need to find ways to divide the design space, such as to create different decks. These games often end up resorting to creating hard divisions between deck types, such as the classes of Hearthstone, or the crafts of Shadowverse. In these games, you gain a renewable mana every turn, but there is no color to it. Instead you choose a hard category of deck, which only has access to certain cards, and usually a shared pool that all decks can access. This means that deckbuilding is typically about optimizing a particular class’s deck, or finding synergies between a group of cards within a deck’s pool of available cards.
Yugioh, which lacks any type of external resource system, eventually converged on “archetypes”, small sets of cards that have incredibly high synergy together. Archetypes typically only extend their effects and searches to other members of that archetype, and only allowing the stronger monsters in the archetype to be summoned using members of the archetype, and sometimes to have more generic compatibility with other card elements, such as type, attribute, or level. This means that there’s no rule saying you can’t put whatever card into your deck, but getting access to cards worth anything is going to be really difficult without playing inside an archetype. The synergy benefits are way too big to ignore.
Since there are no hard limitations on what cards, and therefore archetypes, can be used in a deck, this also means you can mix together multiple archetype “engines” into the same deck, as long as they play well together. This helps give Yugioh a lot of deck-building variety that games with unmixable attributes don’t have. In the screenshot on the left, I’m running cards from the Frog, Nimble, Paleozoic, and Spright engines in the same deck (I have an even more insane list for a deck I haven’t completed that uses P.U.N.K., Ishizu, & Thunder Dragons). The Spright engine is the real play-maker of the deck, but Paleozoic Frogs used to be viable and powerful before Toadally Awesome was banned.
The broader take-away is that Magic’s 5-color Mana system is a very elegant way to separate the design space of a game, before even getting into card type synergies, which is a part of why Magic is such an enduring game and why competitors have a hard time coming up with something as compelling, without simply ripping off Magic’s mana resource system, or implementing something a lot more restrictive. There are of course faults in this style of design, like mana screw and land flood, but it’s remarkably flexible and competent for literally the first trading card game ever.