White cards are "Support Cards", they are neither online (cards which you haven't activated) or offline (cards which you have activated/discarded) in your deck.

White cards automatically activate whenever you have what the requirements met.
such as:
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DigiWindow's effect can be activated more than once during the battle. If you have been damaged then you have recovered HP to full, you may still use its effect.

In short, White cards' effect occurs for the entirety of the battle.
*Some White cards though are merely just for manipulation such as "Lucky Star"

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Green cards, "Luck Cards" also activate automatically. However their effect only occurs only once.
For example:
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Once the automatic effect is activated once requirements are met, this card is now offline.
-Also if you have another Green card in your Deck which also has the same Trigger Effect, as this card for example in the situation above, a "Positron Laser" has the same trigger effect as "Recovery Chance", then you can activate the effects of both cards at the same time in that turn.

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Green & White Cards Similarities:

- Both do not have MP Costs, but their effects will depend on the battle circumstances so it is a bit risky.
- They count toward the number of cards in your Deck.
- Most of their effects will still be activated on your own turn by showing it to your opponent as long as it's effect on the description has been triggered. Some trigger during your opponent's turn even!
- When you have already used a [RED/BLUE/GOLD/BLACK] card on a turn, you can still activate these cards ADDITIONAL effect(s) on that turn since they are non-playable, if the requirements to play them is met.
- Since they are not really playable or directly usable, these cards cannot be selected by certain cards that prevent a Tamer from activate cards, (such as Infinity Tower,) because these card effects are automatically activated.

- Green & White cards are not affected by some card color disabling effects such as
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since they are automatically activated.

If you have any clarifications regarding the Green & White cards, please post here.

*Card which have turned to Green -> White include: Digi-Hazard, Tamer Spirit, Royal Strength, DigiWindow, Lucky Star.

SUMMARY: White cards' effect occurs more than once while
Green cards' effect occurs only once