[Fizzlemizz]

As Xrystal noted, you need to adjust the TH frame from the Blizzard addon, not one you've created.

local function main(self, event, ...)
    local addon = ... -- Check for the addon that has just loaded
    if addon ~= "Blizzard_TalkingHeadUI" then return end -- Not the TH addon so scram
    
    self:UnregisterAllEvents() -- Is the TH addon so we no longer need to check for addons loading
    
    TalkingHeadFrame.BackgroundFrame:SetAlpha(0) -- adjust the TH frame
    TalkingHeadFrame.MainFrame.CloseButton:Hide()
 
    TalkingHeadFrame.NameFrame.Name:SetTextColor(1, 0.82, 0.02)
    TalkingHeadFrame.NameFrame.Name:SetShadowColor(0, 0, 0, 1)
    TalkingHeadFrame.NameFrame.Name:SetShadowOffset(2, -2)
 
    TalkingHeadFrame.TextFrame.Text:SetTextColor(255,255,255)
    TalkingHeadFrame.TextFrame.Text:SetShadowColor(0, 0, 0, 1)
    TalkingHeadFrame.TextFrame.Text:SetShadowOffset(2, -2)
end
 
local f = CreateFrame("Frame") -- frame to listen for the registered event(s)
f:RegisterEvent("ADDON_LOADED")
f:SetScript("OnEvent", main)