In moderate doses melancholy can be strangley comforting, darkly sweet; it can by providing contrast, give an exquisitely sharp edge to happiness, especially to pleasures of the flesh.
Sebastian: By your patience, no. My stars shine darkly over me; the malignancy of my fate might, perhaps, distemper yours; therefore I shall carve of you your leave that I may bear my evils alone. It were a bad recompense for your love to lay any of them on you. - William Shakespeare
I often think of you all, one cannot do what one wants in life. The more you feel attached to a spot, the more ruthlessly you are compelled to leave it, but the memories remain, and one remembers - as in a looking glass, darkly - one's absent friends. - Vincent Van Gogh
Is, then, the crown too heavy that I wear? … Yet it is bright with many a gem; I, the wearer, see not its far flashings; but darkly feel that I wear that, that dazzling confounds. ’Tis Iron – that I know – not gold. - Herman Melville
For now we see through a glass, darkly. - Bible