This word was associated with white flowers for much of Tolkien’s life. In the Qenya Lexicon and Poetic and Mythological Words of Eldarissa of the 1910s, ᴱQ. losse was “rose” (QL/65; PME/56), but in the Early Qenya Grammar of the 1920s its plural was translated as “flowers” (PE14/56), while its gloss became “white-flower” in notes associated with the Earendel poem from around 1930 (PE16/100).
The Etymologies written around 1937, Tolkien derived ᴹQ. losse from the root ᴹ√LOT(H) and translated it as “blossom” or “flower”, but specified that it was “usually, owing to association with olosse snow, only used of white blossom” (Ety/LOT(H); GOLÓS). In notes from around 1959, Tolkien said losse was used of “snow” but also as “the laden inflorescence of flowers on trees or shrubs, especially infoliate or pale” (PE17/161).
Neo-Quenya: For purposes of Neo-Quenya, I would assume lossë mainly meant “snow”, but that it could also be used of white flowers, either an individual white flower or a scattering of white flowers on a plant, as if covered by snow (though in the latter case, I would use plural lossi “white flowers” to be less ambiguous).
lossë (2) noun "blossom" ("usually, owing to association with olosse snow, only used of white blossom") (LOT(H) )