There are many distinctions about the Requiem Mass. Most notably the sombre choice of black vestments, the simple stripped down Kyriale without any organ accompaniment and the absence of flowers on the altar. Something that can go unnoticed at times is the use of yellow, unbleached beeswax candles.
What is the symbolic meaning of their usage?
The matter is, to some degree, one of common sense. Historically in the Roman and Eastern liturgy, white and gold colors lean towards festive and joyful occasions and the more sombre colors of violet and black reflect mourning and sombre tones. Likewise, "The employment on occasions of sorrow (the Tenebrae, funerals, etc.) of unbleached rather than bleached candles is evidently fitting, since the sombre tones of unbleached wax harmonize with the mournful ceremony, while bleached wax, being far higher in the tone scale, would intrude a note of joy." 1
Another interesting element about beeswax is that at the moment it is secreted from the glands of the underside of the virgin honeybee the wax is translucent and pure white in color. The young, female virgin worker bees are responsible for producing and then engineering the honey comb structure within the hive during their first week or two of their life. The production of new, white wax only occurs when there is a surplus of incoming nectar (typically spring) as the wax glands within each bee are fueled by the consumption of nectar and pollen on the order of 8 pounds of nectar for every 1 pound of wax secreted.
Within the life time of one generation in the colony (30-40 days) the once white beeswax changes color to a golden yellow or yellowish orange hue due being stained with the oil residue left behind by the pollen granules coating the body of the bees. This is especially noticeable in the late summer and fall with asters, golden rod and other wildflowers with deep yellow and purple in bloom throughout the northern hemisphere. When the beekeeper harvest the honey and wax - and processes them, any white wax that is processed with the stained yellow wax ultimately takes on the yellow tone because beeswax is soluble in oil. To return beeswax to its virginal white color, the wax is typically bleached with concentrated technical grades of peroxide or through an elaborate sun bleaching system.
Taking these considerations in the the context of candles and the liturgical seasons we can draw new parallels from the life of the hive and production of the color of the wax. Most notably that the white wax used for solemn feasts and the season after Pentecost is associated with the new birth of the virgin bees (baptism/easter/ordinations) and the fresh nectar needed to produce this white wax could be linked to the sweetness of life and festivity. The yellow wax used for sombre liturgical seasons and celebrations could be tied to a maturity/age and or the seasonal death of fall and winter when the darker pollen oil residues are present in the wax.
1 Candles in the Roman Rite by Fr. Edwin Ryan, DD 1934
2 Liturgical Imagines courtesy of www.liturgicalartsjournal.com