Unfortunately on Good Friday only red is listed as an option in the rubrics of the modern Roman missal. I would propose this is a task for the reform of the reform -- to restore, at very least, an option for black vestments to be used on Good Friday.
In the usus antiquior pictures that you will no doubt see here on the NLM today, black vestments are what are specified. The Catholic Encyclopedia explains it this way:
A black fast, black vestments, a denuded altar, the slow and solemn chanting of the sufferings of Christ, prayers for all those for whom He died, the unveiling and reverencing of the Crucifix, these take the place of the usual festal liturgy; while the lights in the chapel of repose and the Mass of the Presanctified is followed by the recital of vespers, and the removal of the linen cloth from the altar ("Vespers are recited without chant and the altar is denuded").
Obviously red is a colour we in the West associate with two things in particular: Pentecost and Martyrs. As regards the latter, the association is specifically made to the blood of martyrs, so this would seem to be the relevant symbolic tie-in between Christ's Passion and death and red vestments.
But I have often proposed that black is, culturally (at least in the West), an arguably more potent symbol of mourning and sorrow than either purple for funerals (let alone white, but for the case of infants) or red for Good Friday. I have therefore encouraged each year a revival of the use of black in the modern form of the Roman liturgy (where that option is given of course).
It strikes me that the Good Friday liturgy is oriented toward the somber expression of sorrow for Christ's Passion and Death, complete with prostrations, a stripped altar, an absent Eucharistic Lord, veiled images and so forth. The Lord is, symbolically, in the tomb. He is dead; "[he] was crucified also for us under Pontius Pilate, suffered and was buried". One can see why black, a symbol of death, sorrow and mourning, was used, and perhaps also why it should again be allowed, at very least as an option, in the modern Roman liturgy.
Now proposing black might be a more potent cultural and liturgical symbol suited to the liturgical symbolism of Good Friday is one thing, and saying red is inappropriate is entirely another. So let me be clear that I am not arguing that red as a liturgical colour for Good Friday is inappropriate. I think one can make the case that there are indeed also relevant, symbolic tie-in's to the symbolism of blood shed for some greater, heavenly purpose.
That said, black has been our Roman rite tradition on this day for some time and I think this element of continuity with tradition cannot be lost and bears with it a relevance and value in and of itself, particularly if we take the hermeneutic of continuity into account.
Likewise, the fact that black bears such unique and strong symbolic associations with the aforementioned themes of death and mourning makes it particularly well-suited to the tone of the Good Friday liturgy and is perhaps also very didactically suited to instructing people about the sorrow we should feel at Christ's Passion and Death for our sins; the torture and death of the Son of God; the spotless Lamb.
Bearing these reasons in mind, while I should be delighted were the Pope to restore black as the usage for both forms of the Roman liturgy for this day, at very least I believe that black should be restored as an option for the modern Roman liturgy.
Perhaps that will be part of the "mutual enriching" that the Pope spoke of in Summorum Pontificum.
