There’s a grade school picture of my Dad where his hair is a bright blond.
That’s certainly not the way I remember it. As long as I can remember it was black.
When researching your relative ask yourself:
what about them could have changed over time?
It could have been more than their hair color. It could have been their occupation, their marital status, their economic status, their religion, etc. Those changes could explain why they cannot be located in certain records, in a certain place, etc. Some changes are obvious. Others are not.
Depending upon how many of those changes we have had in our own lives it may be easier to see how similar ones could have impacted our relatives. If we’ve not experienced those changes, it can sometimes be more difficult to see how they might have impacted our “lost ancestors.”
Loss of hair really doesn’t impact finding our ancestors. This comes from personal experience. There are some changes that really don’t matter. Hair loss is one of those. I need to remember that.