Robusto's answer is correct, I'm just adding another thought.
Is this a case of people making a grammatical mistake or are both forms completely correct and it's just a matter of preference?
Robusto didn't quite address that question head on. While there is a lot of flexibility in punctuation, I would say any professional editor worth his or her salt would correct 'white bearded' to 'white-bearded'. Leaving out the hyphen is not optional.
Yes, in informal contexts, writers very often leave out the hyphens, either because they are unsure how to use them, or they forget. But that's not the same as saying they are optional. They are making a mistake which can lead to misunderstandings, and knowing how and why to use hyphens in compound adjectives places you at an advantage.
Finally, often with punctuation, we say "well, it doesn't exist in spoken English, so is it really required?"
But in spoken English there is an audible difference between
The white, bearded man.
The white-bearded man.
It's subtle, but it's there, and it makes all the difference to the interpretation of the sentence.