Srimad Bhagavatam Canto 10, Chapter 03, Text 20

SB 10.3.20

sa tvam tri-loka-sthitaye sva-mayaya
 bibharsi suklam khalu varnam atmanah
sargaya raktam rajasopabrmhitam
 krsnam ca varnam tamasa janatyaye
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
My Lord, Your form is transcendental to the three material modes, yet for the maintenance of the three worlds, You assume the white color of Visnu in goodness; for creation, which is surrounded by the quality of passion, You appear reddish; and at the end, when there is a need for annihilation, which is surrounded by ignorance, You appear blackish.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Vasudeva prayed to the Lord, “You are called suklam. Suklam, or ‘whiteness,’ is the symbolic representation of the Absolute Truth because it is unaffected by the material qualities. Lord Brahma is called rakta, or red, because Brahma represents the qualities of passion for creation. Darkness is entrusted to Lord Siva because he annihilates the cosmos. The creation, annihilation and maintenance of this cosmic manifestation are conducted by Your potencies, yet You are always unaffected by those qualities.” As confirmed in the Vedas, harir hi nirgunah saksat: the Supreme Personality of Godhead is always free from all material qualities. It is also said that the qualities of passion and ignorance are nonexistent in the person of the Supreme Lord.
In this verse, the three colors mentioned — sukla, rakta and krsna — are not to be understood literally, in terms of what we experience with our senses, but rather as representatives of sattva-guna, rajo-guna and tamo-guna. After all, sometimes we see that a duck is white, although it is in tamo-guna, the mode of ignorance. Illustrating the logic called bakandha-nyaya, the duck is such a fool that it runs after the testicles of a bull, thinking them to be a hanging fish that can be taken when it drops. Thus the duck is always in darkness. Vyasadeva, however, the compiler of the Vedic literature, is blackish, but this does not mean that he is in tamo-guna; rather, he is in the highest position of sattva-guna, beyond the material modes of nature. Sometimes these colors (sukla-raktas tatha pitah) are used to designate the brahmanas, ksatriyas, vaisyas and sudras. Lord Ksirodakasayi Visnu is celebrated as possessing a blackish color, Lord Siva is whitish, and Lord Brahma is reddish, but according to Srila Sanatana Gosvami in the Vaisnava-tosani-tika, this exhibition of colors is not what is referred to here.
The real understanding of sukla, rakta and krsna is as follows. The Lord is always transcendental, but for the sake of creation He assumes the color rakta as Lord Brahma. Again, sometimes the Lord becomes angry. As He says in Bhagavad-gita (16.19):
tan aham dvisatah kruran
 samsaresu naradhaman
ksipamy ajasram asubhan
 asurisv eva yonisu
“Those who are envious and mischievous, who are the lowest among men, are cast by Me into the ocean of material existence, into various demoniac species of life.” To destroy the demons, the Lord becomes angry, and therefore He assumes the form of Lord Siva. In summary, the Supreme Personality of Godhead is always beyond the material qualities, and we should not be misled into thinking otherwise simply because of sense perception. One must understand the position of the Lord through the authorities, or mahajanas. As stated in Srimad-Bhagavatam (1.3.28), ete camsa-kalah pumsah krsnas tu bhagavan svayam.
Srimad Bhagavatam Canto 10, Chapter 03, Text 19
Srimad Bhagavatam Canto 10, Chapter 03, Text 21