So my buggrabber is spamming me with this lua-error. Maybe it helps.

9x Kui_Enemy_Colors\custom-Custom.lua:136: attempt to call method 'SetBackdrop' (a nil value)
[string "@Kui_Enemy_Colors\custom-Custom.lua"]:136: in main chunk

Locals:
folder = "Kui_Enemy_Colors"
ns =

{
}
addon = {
NAME_PLATE_UNIT_REMOVED = defined @Kui_Nameplates\addon.lua:117
ui_print = defined @Kui_Nameplates\addon.lua:59
DispatchMessage = defined @Kui_Nameplates\messages.lua:108
Frames = defined @Kui_Nameplates\addon.lua:62
NewElement = defined @Kui_Nameplates\messages.lua:564
NewPlugin = defined @Kui_Nameplates\messages.lua:527
plugins = {
}
GetPlugin = defined @Kui_Nameplates\messages.lua:557
layout = {
}
NAME_PLATE_UNIT_ADDED = defined @Kui_Nameplates\addon.lua:93
MINOR = 5
GetActiveNameplateForUnit = defined @Kui_Nameplates\addon.lua:71
NamePlateDriverFrame_AcquireUnitFrame = defined @Kui_Nameplates\hook.lua:21
Nameplate = {
}
Layout = defined @Kui_Nameplates\messages.lua:571
GetNameplateForGuid = defined @Kui_Nameplates\addon.lua:77
PrintTrace = defined @Kui_Nameplates\messages.lua:88
0 =
UI_SCALE_CHANGED = defined @Kui_Nameplates\addon.lua:135
NAME_PLATE_CREATED = defined @Kui_Nameplates\addon.lua:86
MAJOR = 2
PLAYER_LEAVING_WORLD = defined @Kui_Nameplates\addon.lua:126
print = defined @Kui_Nameplates\addon.lua:55
DEBUG_IGNORE = {
}
HookNameplate = defined @Kui_Nameplates\hook.lua:27
GetNameplateForUnit = defined @Kui_Nameplates\addon.lua:65
}
core = {
OnEnter = defined @Kui_Nameplates_Core\hook.lua:152
Scale = defined @Kui_Nameplates_Core\config.lua:272
CreateNameOnlyGlow = defined @Kui_Nameplates_Core\create.lua:2125
AurasButton_SetFont = defined @Kui_Nameplates_Core\create.lua:1800
LSMMediaRegistered = defined @Kui_Nameplates_Core\create.lua:297
NameOnlyUpdate = defined @Kui_Nameplates_Core\create.lua:2329
CreateAuras = defined @Kui_Nameplates_Core\create.lua:1652
LostTarget = defined @Kui_Nameplates_Core\hook.lua:129
layout = true
Create = defined @Kui_Nameplates_Core\hook.lua:23
GainedTarget = defined @Kui_Nameplates_Core\hook.lua:117
CreateHighlight = defined @Kui_Nameplates_Core\create.lua:458
QuestUpdate = defined @Kui_Nameplates_Core\hook.lua:162
ShowNameUpdate = defined @Kui_Nameplates_Core\create.lua:2061
InitialiseElements = defined @Kui_Nameplates_Core\create.lua:2338
Auras_PostCreateAuraButton = defined @Kui_Nameplates_Core\create.lua:1700
HealthColourChange = defined @Kui_Nameplates_Core\hook.lua:93
CreateThreatBrackets = defined @Kui_Nameplates_Core\create.lua:2014
configChangedStateIcons = defined @Kui_Nameplates_Core\create.lua:1472
CreateGuildText = defined @Kui_Nameplates_Core\create.lua:839
PowerTypeUpdate = defined @Kui_Nameplates_Core\hook.lua:99
CreateQuestIcon = defined @Kui_Nameplates_Core\create.lua:2049
InitialiseFadeRules = defined @Kui_Nameplates_Core\hook.lua:315
SetAurasConfig = defined @Kui_Nameplates_Core\create.lua:1809
SetLocals = defined @Kui_Nameplates_Core\create.lua:222
configChangedTextOffset = defined @

This is coming from another addon, "Kui_Enemy_Colors", which hasn't been updated for shadowlands. That's not an addon I made so I can't fix it. Its last update was in 2017.

You can achieve the same behaviour, but without an interface in game, with this custom script. Of course you'll have to edit the list of names to colours and, uh, yeah. it's not as user-friendly.