Dusk has two meanings in love. One is to represent the yellow love, yellow love generally refers to the love of older people. The second is to miss, because "Xiao see the sky at night to see the clouds, line also think of you, sit also think of you", if someone sends you a photo at dusk, it means that you miss you.
First, on behalf of yellow love
Dusk represents the meaning of acacia from (Ming) Tang Yin "a plum · Rain hit pear deep behind the door", there is a sentence "Xiao see the sky at night to see clouds, line also think of you, sit also think of you", meaning from morning to evening has been looking at the sky clouds, walking miss you, sitting also miss you. So in love, if someone sends you a picture at dusk, it means that the other person is missing you.