Timing of Persecution

[Zuriya]

Edit: The card I meant was Persecute.

When is the choice of color made ? When I announce the spell or when it resolves ? This matters as i wanted to copy [cardname]Persecute[/cardname].

409.1b If the spell or ability is modal (uses the phrase "Choose one -," "Choose two -,"or "[specified player] chooses one -"), the player announces the mode choice. If the player wishes to splice any cards onto the spell (see rule 502.40), he or she reveals those cards in his or her hand. If the spell or ability has a variable mana cost (indicated by {X}) or some other variable cost, the player announces the value of that variable at this time. If the spell or ability has alternative, additional, or other special costs (such as buyback, kicker, or convoke costs), the player announces his or her intentions to pay any or all of those costs (see rule 409.1f). You can't apply two alternative methods of playing or two alternative costs to a single spell or ability. Previously made choices (such as choosing to play a spell with flashback from his or her graveyard or choosing to play a creature with morph face down) may restrict the player's options when making these choices.

409.1c If the spell or ability requires any targets, the player first announces how many targets he or she will choose (if the spell or ability has a variable number of targets), then announces the targets themselves. A player can't play a spell or ability unless he or she chooses the required number of legal targets. The same target can't be chosen multiple times for any one instance of the word "target" on the spell or ability. If the spell or ability uses the word "target" in multiple places, the same object, player, or zone can be chosen once for each instance of the word "target" (as long as it fits the targeting criteria).

It doesn't say ""Choose one -," "Choose two -,"or "[specified player] chooses one -" so I am uncertain.

Thanks
Edit: Of course the cardname is Persecute (grr).

[Nightmare]

You choose a color upon the resolution of the spell, the same as naming a card with Cabal Therapy. Choosing a color is not the same thing as a modal spell. Compare this:

Persecute
2BB (4), Sorcery
Choose a color. Target player reveals his or her hand and discards all cards of the chosen color.

with this:

Primal Command
3GG (5), Sorcery
Choose two - Target player gains 7 life; or put target noncreature permanent on top of its owner's library; or target player shuffles his or her graveyard into his or her library; or search your library for a creature card, reveal it, put it into your hand, then shuffle your library.

[Zuriya]

Cool, thanks.
Edit: the wording has to be exactly as in the quotation.