PetTracker-10.0.1 for WoW-10.0.2
Got this erorr message when starting wow.
Seems to be linked to Kalieltracker as well as when I got this issue, Kaliel tracker stop refreshing quests list.
Deactivating Pettracker solve my issue.

["message"] = "...PetTracker/addons/main/classes/tracking/textLine.lua:53: attempt to perform arithmetic on field 'r' (a table value)", ["time"] = "2023/02/08 09:55:39", ["stack"] = "[string \"@Interface/AddOns/PetTracker/addons/main/classes/tracking/textLine.lua\"]:53: in function HighlightColor'\n[string "@Interface/AddOns/PetTracker/addons/main/classes/tracking/textLine.lua"]:32: in function <...PetTracker/addons/main/classes/tracking/textLine.lua:21>\n[string "=(tail call)"]: ?\n[string "@Interface/AddOns/PetTracker/addons/main/classes/tracking/textList.lua"]:29: in function Add'\n[string \"@Interface/AddOns/!KalielsTracker/Modules/Addon_PetTracker.lua\"]:72: in function AddSpecie'\n[string "@Interface/AddOns/PetTracker/addons/main/classes/tracking/tracker.lua"]:58: in function AddSpecies'\n[string \"@Interface/AddOns/!KalielsTracker/Modules/Addon_PetTracker.lua\"]:61: in function Update'\n[string "@Interface/AddOns/!KalielsTracker/Modules/Addon_PetTracker.lua"]:53: in function ?'\n[string \"@Interface/AddOns/PetTracker/libs/CallbackHandler-1.0-8/CallbackHandler-1.0.lua\"]:119: in function <...ker/libs/CallbackHandler-1.0/CallbackHandler-1.0.lua:119>\n[string \"=[C]\"]: ?\n[string \"@Interface/AddOns/PetTracker/libs/CallbackHandler-1.0-8/CallbackHandler-1.0.lua\"]:29: in function <...ker/libs/CallbackHandler-1.0/CallbackHandler-1.0.lua:25>\n[string \"@Interface/AddOns/PetTracker/libs/CallbackHandler-1.0-8/CallbackHandler-1.0.lua\"]:64: in function Fire'\n[string "@Interface/AddOns/PetTracker/libs/AceEvent-3.0-4/AceEvent-3.0.lua"]:120: in function <...AddOns/PetTracker/libs/AceEvent-3.0/AceEvent-3.0.lua:119>",
["session"] = 7268,
["counter"] = 18,`

This is definitely related to Kaliel's Tracker.
I'm getting the same error when both KT and PT are enabled AND PT support in KT is toggled on.
There is no way to get the Pets Objective to show when KT is enabled. It shows fine when KT is disabled and the error won't pop up when PT support is toggled off but then the Pets Objective is not shown.

Edit: Commenting out the problematic line seems to fix the problem but I have no idea what other consequences this might have.

You cannot distribute fixes for Kaliels Tracker due to its license, however you can locally modify it for yourself. To fix this error change line 70 in Modules/AddOn_PetTracker.lua from

local r,g,b = self:GetColor(quality) to

local r,g,b = self:GetColor(quality):GetRGB()

Thanks for this workaround, that gets rid of the error and restores most of the functionality.
I have created a ticket for KT:
https://www.curseforge.com/wow/addons/kaliels-tracker/issues/706