Color balance
The color balance of a deck refers to the interaction of two parts of that deck. The first part is the deck's mana sources and their colors. The second part is the deck's mana costs and their colors.
Color slots
Color slots refer to a technique that evaluates how much of a deck's mana base is required to support a color on a given turn. The technique is best explained by examples.
For now, let us consider a deck using a basic curve, as referred to in "mana curve", and only basic lands. Let us start with "60 cards, play first". In these decks, we have a starting point of 24 lands. The second turn slot requires at least 12 lands that produce that color for a 90% probability to cast[1], and a third turn slot requires 11 lands - conveniently adding up to just under 24 lands. A 12/12 manabase would thus be perfectly functional for a two-color deck, assuming there are no 1-drops that need to be played on the first turn.
If this deck wanted to use double colored mana costs then it would have to dedicate 20 sources to support the cost on turn two, 17 to support on turn 3, or 15 to support it on turn 4. For a two-color deck with CC and 1D costs, this would require a total of 32 sources, which necessitates the usage of at least eight dual lands to function properly, and with only basics means a 57% probability to cast a CC spell on the second turn. A deck with CC and DD costs would need 40 total sources and 16 dual lands, which ranges from difficult to impossible depending on the format. For triple cost or above this gets even more restrictive. Triple cost on turn three would require 22 land, or turn four would require 18. For both of these, a manabase using only basics can only support one color, as the remaining lands will have almost consistency of supporting any cards on the curve.
"Reverse Mana Syndrome"
Some cards can be so powerful in a deck that players can actually "reverse" the normal way that the colors are represented with lands. If for example a black card is powerful enough to win the game as soon as it is played (or soon after) it will be crucial to have that mana. If the deck has 36 red spells and 4 of these black spells it can be necessary to play with 8 mountains and 16 swamps. Players rarely use this syndrome, even though it is vital in a few odd decktypes.
Manipulating the color balance
Besides finding a perfect mix of colors and mana generators there are plenty of ways to twist the balance even further.
- Artifacts: Cards needing no color cause no color problems.
- Hybrid cards: The fact that these cards may be played from any mix of the it's hybrid colors mean that it is very easy to play such cards, especially if the deck is only two-colored.
- Morph: The ability Morph enables some cards to be played without the use of colored mana. Later they can be activated by the relevant colored mana.
- Multicolored: Few people realize this, but in a deck with two colors and an even amount of the two colors of mana it is far more likely that you can play a multicolored card (Example: Meddling Mage) before you can cast a full-colored card (Example: White Knight). The reason for this is purely statistical. Using such knowledge may press the color balance to the edge of what is mathematical possible.
- Split cards: Increases the chances of casting a spell for the available mana. If the first card of the "split" cannot be cast, there is always a chance that the second may.