In the Qenya Lexicon of the 1910's there is a word called lómë (I:255). This is the first occurance of such a word that I am aware of. There the word is translated as 'dusk, gloom, darkness'. This word was also used in some compounds: "Hisilómë (and this means 'Shadowy Twilights')" (I:112), "the name Wirilóme of the great spider" (I:254). The root of the word was then LOMO (I:255). Based on these compounds, the connotations of the word were most likely quite evil then.
These connotations probably continued to exist until the era of The Etymologies, for the word occurs in a plural compound form mandulómi (MC:221), which doesen't occur as such in the free translation, but the corresponding line goes thus: "...the East raised black shadows out of Hell." (MC:221). It is probably formed from #mandu "hell" (cf. "Angamandu or Eremandu 'Hells of Iron' [I:249]) lóme, to fit the meaning.
But a complete revision happened in the latter half of the 30s. In The Lost Road Alboin states that "..certainly lómë is night (though not darkness)" (V:41). But although The Etyomologies and The Lost Road are from around the same time, lóme is defined in the entry DO3-, DÓ-: "Night, night-time, shades of night" (V:354), which seems to imply something not quite so positive. There are also several more explicitly bad connotations in its cognates, but suprisingly also lómelinde "nightingale", which is a good bird for the Eldar: Lúthien's other name Tinúviel means "nightingale" (V:393). The root of the word was then DO3-, DÓ- (V:354).
Compound words with lóme entered LR in 1943: Aldalóme (VII:420), Tauremornalóme (implied in VII:417) and lómeamor (VII:419). Aldalóme and Tauremornalóme do not necessarily anything imply evil, they are probably neutral, because lóme has an negative definition in morna "gloomy, sombre" (V:373): if it were already that it wouldn't need it. At this stage even #lómea in lómeamor might not have an evil definition because of the following mor"darkness" (L:308), but this is not entirely clear. If it was ever so, it was evidently changed later: see the sixth paragraph.
The above statements that Tolkien had no evil connotations in his mind for lóme in that stage is supported Lowdham's Report on the Adunaic Language from the mid-40s, close to the making of the Fangorn-chapter: "...the Adunaic word lómi 'night' is an Avallonian lone; both because of its sense (it appears to mean 'fair night, a night of stars', with no connotations of gloom or fear)..." (IX:414). "Gloom" in its meaning is utterly denied here, if only through byway, even though lómë was thus defined in QL. The root of the word was then LOM, and it had a stem lómi- (IX:415). This stem seems clashes with lómelinde "nightingale" (V:354) and lómelindi "nightingales" (X:172), but agrees with Lóminórë (X:145).
In Appendix F, which was written during the period between the completion of LR propper and its publication, and updated in the second edition, Tolkien said that the Entish stanza "Taurelilómëa-tumbalemorna Tumbaletaurëa Lómëanor" (LR:1105) "may be rendered 'Forestmanyshadowed-deepvalleyback Deepvalleyforested Gloomyland" and that it "..meant more or less: 'there is a black shadow in the deep dales of the forest'". #Lómëa "shadowed, gloomy": a return to the meaning of the QL, and a denial of the statements in V:41 and IX:414. Here lóme does have evil connotations.
Lómelinde still existed in the later 50's (X:172): this conflicts with the upper paragraph unless lóme had both surely evil connotations in some words and purely good in others. Lóme was simply glossed "night" in a letter from 1961 (L:1961).
It can be seen that the history of the word lóme is as tanglely as a tree in Fangorn: it can be either bad or good, but it isn't necessarily in anybody's side.