Col 4:15
Greet the brothers who are in Laodicea, and to Nympha and the church that is in her house. (NHEB)
Greet the brethren in Laodicea, and Nymphas, and the church in his house. (SLT)
The original Greek Colossians 4:15, shows that Nymphas is marked as "N-ASM", and (if you select it) shows that it means "Noun — Accusative Singular Masculine".
So Nymphas was a male, at least according to the manuscripts that the KVJ and others are based on.
Compare with Romans 16:15, where both men and women are named, and their names are accordingly marked (e.g. Julia is "N-ASF").
On the other hand, some old manuscripts (e.g. the NU-Text) have the feminine form of the name, "Nympha", and "her".
The problem occurs because the accusative forms of the two names have exactly the same spelling, the only difference being in an accent mark. The oldest manuscripts didn't use accent marks, which were added many years later.
Such basic textual variant issues should be answered easily from the NET Bible notes. You can access it on netbible site or on stepbible:
4:15 tc If the name Nympha is accented with a circumflex on the ultima (Νυμφᾶν, Numfan), then it refers to a man; if it receives an acute accent on the penult (Νύμφαν), the reference is to a woman. Scribes that considered Nympha to be a man’s name had the corresponding masculine pronoun αὐτοῦ here (autou, “his”; so D [F G] Ψ Ï), while those who saw Nympha as a woman read the feminine αὐτῆς here (auth", “her”; B 0278 6 1739[*] 1881 sa). Several mss (א A C P 075 33 81 104 326 1175 2464 bo) have αὐτῶν (autwn, “their”), perhaps because of indecisiveness on the gender of Nympha, perhaps because they included ἀδελφούς (adelfou", here translated “brothers and sisters”) as part of the referent. (Perhaps because accents were not part of the original text, scribes were particularly confused here.) The harder reading is certainly αὐτῆς, and thus Nympha should be considered a woman.
The later variants includes his and their; the oldest and harder reading leads to her. The scribes might have included "brothers" of both referrants in writing "their" instead of her. The SLT version follows the later bad mss like all old bibles, while Godbey version has "their". Thus, Nympha is a woman.
There is a divergence of the textual tradition in Col 4:15; the two dominant readings being:
1. NA28/UBS5, W&H (ie, earliest MSS):
Νύμφαν καὶ τὴν κατ’ οἶκον αὐτῆς ἐκκλησίαν = Nymphan [fem] and the congregation that meets in her house
2. Byzantine (ie, medieval MSS):
Νυμφᾶν, καὶ τὴν κατ’ ο ἴκον αὐτοῦ ἐκκλησίαν = Nymphan [masc] and the congregation that meets in his house
For details about what MSS support which tradition (and some other variants) see UBS5.
APPENDIX - Female Bible leaders
The fact that early NT MSS have Nymphas as feminine is consistent with other female Bible leaders, eg,