Okay I was really thinking and eyeing the Nian and Pina (Nina and Paul) EW picture. @Laynaa asked if anyone thinks there's a reason that Nian is White and Pina is Black.
I looked it over and did some searchings and thinking on the subject.

White

White projects PURITY, innocence, virginity, cleanliness, and neutrality. Doctors don white coats, brides traditionally wear white gowns and a white picket fence surrounds a veilig and HAPPY home.

So I think for DE it means: that their relationship is pure. True relationship is absolutely free from self interest. It is always dedicated with no expectation at all in return. Only to help.
They are veilig in each which is why Nina (Elena) doesn't have a bra on with Ian (Damon) and does have one with Paul (Stefan). She feels so veilig with him (Ian) that she gives herself to him completly with no turning back. While with Paul (Stefan) she doesn't trust him enough to give her self to him completly, hence the bra.

White: It is good for NEW BEGINNINGS, enthusiasm, clarity of purpose, spiritual insights and inspiration.
White often reminds us of Heaven with angels dancing among the clouds in white flowing gowns and white wings. It is considered to be the color of PERFECTION.
White means SAFETY, STRENGTH, and cleanliness. White INCREASES THE FLOW OF THE LIFE FORCE.

It's a new beginning for DE. They are fogetting all their past and starting together their "rebirth"

The color white heals the body, mind and spirit at al levels. White means kindness. It stands for WHOLENESS and COMPLETION. Represents openness and TRUTH.
White is the perfect color; for it is all colors, in PERFECT balance and HARMONY.

Wholeness and completion- Being in a state of wholeness means completely free of wound of injury with nothing missing and everything complete, perfect, unbroken, and uncut; perfectly healthy and free of any defect, deformity, mistake of impairment having all its proper parts and components.

Sure DE is not perfect and do have some defects, but they have all the characteristics of pure love: trust, selfless, comfort, ect.
Love always win, meaning that love never fails. Love always survives. And DE has showed that door surviving all the obsticals thrown at them.

Whire: Brides wear white in many countries, because white symbolizes a virgin. White daisies are a symbol of LOYAL LOVE.
White is also associated with heroism and GOODNESS.
It is the color of the AWAKENED SPIRIT; the LIGHT of PERFECTION; the light of the Cosmic Consciousness, the Divine Light. Just about everyone has heard of surrounding people with the "White Light of Healing and PROTECTION."
As opposed to black, white usually has a positive connotation. Strictly speaking, white is not a color, but the manifestation of the presence of all color - THE COMPLETE ENERGY OF LIFE.

Notice the words in bold and think about DE's relationship.

Black

Black is the color of the night, and of "evil."
Black can also represent ideas such as power, sexuality, sophistication, formality, wealth, mystery, FEAR, evil, UNHAPPINESS, depth, style, SADNESS, REMORSE, ANGER, and MOURNING. Black can also represent a LACK OF COLOR, the PRIMORDIAL VOID, EMPTINESS. It can also mean SORROW of mourning, in the Christian tradition of wearing black to funerals.

Notice the words "sorrow, unhappiness, sadness, remorse, mourning, emptiness, and primordial void"

That's saying something for SE. I'm not going to go on how these words say something for SE but I'll give a few examples.

Lack of color- Which can also mean lack of life of lifeless. If a couple is lifeless and is lacking color then u can tell that their relationship is not alive and it's missing something. It's dead and unpassionate.

Emptiness- they relationship is empty unlike DE's. Sure they are together but they are missing something in their relationships making them almost empty.
I'll stop right there because the rest might be a rant.
But this is saying something about their choise for the couples photos.

Look at DE is White and the things that White means, then look at Black and SE and see if u can make the connection to them and the colors they are matched with.