[Fizzlemizz]

The conditions could look something like:

if event == "PLAYER_TARGET_CHANGED" then
    local FactionTextures = {
        Alliance = "Interface\\AddOns\\[TextureLocation]\\AllianceTexture",
        Horde = "Interface\\AddOns\\[TextureLocation]\\HordeTexture",
        FFA = "Interface\\AddOns\\[TextureLocation]\\NeutralTexture",
    }
    local player = UnitIsPVPFreeForAll("player")
    local target = UnitIsPVPFreeForAll("target")
    if player and target then -- both are FFA, maybe this is all you need.
        -- Set the texture to FactionTextures.FFA
        -- show the frame
        return
    end
    player = UnitFactionGroup("player")
    target = UnitFactionGroup("target")
    if player ~= target and target ~= "Neutral" then
        -- set the texture to FactionTextures[target]
        -- show the frame
    else -- target is same faction or neutral
        -- hide the frame
    end
end