Celestial Dawn — ruling 1

If a nonbasic land has an ability that causes it to enter the battlefield tapped, it will lose that ability before it applies. The same is also true of any other abilities that modify how a land enters the battlefield or apply "as" a land enters the battlefield, such as the first ability of Cavern of Souls.

Celestial Dawn — ruling 2

Mana produced by spells you control and nonland permanents you control isn't affected by Celestial Dawn. Llanowar Elves will produce {G}, for example. However, any colored mana may be spent only on the colorless part of costs.

Celestial Dawn — ruling 3

Land cards you own that aren't on the battlefield aren't changed to Plains.

Celestial Dawn — ruling 4

If you have unspent nonwhite mana when Celestial Dawn enters, you still have that mana, but you can spend it only on the colorless part of costs.

Celestial Dawn — ruling 5

If you use a text-changing effect such as Mind Bend on Celestial Dawn to change the word "Plains" to a different land type, your lands are all of that new land type, and they will produce mana of the appropriate color for that type.

Celestial Dawn — ruling 6

If a permanent enters while Celestial Dawn is on the battlefield, and then Celestial Dawn leaves the battlefield, the permanent's color will revert to the colors in its mana cost.

Celestial Dawn — ruling 7

The effect to turn all your non-land cards (including artifacts) white is the effect of a static ability. Thus, a color change on a permanent prior to Celestial Dawn entering the battlefield will be overridden by Celestial Dawn's effect.

Celestial Dawn — ruling 8

Celestial Dawn does not change the type of lands which are not on the battlefield. Lands not on the battlefield are what they say they are.

Celestial Dawn : règles, fonctionnement et interactions (MTG)

Celestial Dawn is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Lands you control are Plains. Nonland permanents you control are white. The same is true for spells you control and nonland cards you own that aren't on the battlefield. You may spend white mana as though it were mana of any color. You may spend other mana only as though it were colorless mana.

How it works : Celestial Dawn

Original English text — Wizards of the Coast / Scryfall

#1September 29, 2017· Wizards of the Coast
If a nonbasic land has an ability that causes it to enter the battlefield tapped, it will lose that ability before it applies. The same is also true of any other abilities that modify how a land enters the battlefield or apply "as" a land enters the battlefield, such as the first ability of Cavern of Souls.
No other card is named in this ruling.
#2September 25, 2006· Wizards of the Coast
Mana produced by spells you control and nonland permanents you control isn't affected by Celestial Dawn. Llanowar Elves will produce , for example. However, any colored mana may be spent only on the colorless part of costs.
No other card is named in this ruling.
#3September 25, 2006· Wizards of the Coast
Land cards you own that aren't on the battlefield aren't changed to Plains.
No other card is named in this ruling.
#4September 25, 2006· Wizards of the Coast
If you have unspent nonwhite mana when Celestial Dawn enters, you still have that mana, but you can spend it only on the colorless part of costs.
No other card is named in this ruling.
#5September 25, 2006· Wizards of the Coast
If you use a text-changing effect such as Mind Bend on Celestial Dawn to change the word "Plains" to a different land type, your lands are all of that new land type, and they will produce mana of the appropriate color for that type.
No other card is named in this ruling.
#6September 25, 2006· Wizards of the Coast
If a permanent enters while Celestial Dawn is on the battlefield, and then Celestial Dawn leaves the battlefield, the permanent's color will revert to the colors in its mana cost.
No other card is named in this ruling.
#7October 4, 2004· Wizards of the Coast
The effect to turn all your non-land cards (including artifacts) white is the effect of a static ability. Thus, a color change on a permanent prior to Celestial Dawn entering the battlefield will be overridden by Celestial Dawn's effect.
No other card is named in this ruling.
#8October 4, 2004· Wizards of the Coast
Celestial Dawn does not change the type of lands which are not on the battlefield. Lands not on the battlefield are what they say they are.
No other card is named in this ruling.
#9October 4, 2004· Wizards of the Coast
Will not add or remove Snow Supertype from a land.
No other card is named in this ruling.
#10October 4, 2004· Wizards of the Coast
You may use a different color mana than the color required for spells and abilities that require a specific color. If you do, and the spell or ability checks the actual color of the mana, it can tell the difference.
No other card is named in this ruling.
#11October 4, 2004· Wizards of the Coast
If you pay white mana to activate an ability that can only be activated by spending another color of mana, then any limitations on activating the ability (such as the number of times it can be activated each turn) still apply as if you spent the proper color.
No other card is named in this ruling.
#12October 4, 2004· Wizards of the Coast
Celestial Dawn no longer changes mana symbols on cards.
No other card is named in this ruling.