Yep you are right but without a scope there is not much else to look for.There is no way to tell by simply looking at a plant. Anyone who tells you differently has no idea what they are talking about.
You cannot go by hairs either. I have seen plants with solid white hairs with amber trichs, and I have seen strains with every hair receded and red/orange and still mostly clear/some cloudy trichs.
Pros use scopes, only a straight up newb thinks they can look at a plant and know if it is mature.