I think some of the confusion comes from the mental picture of Jensen. He has been around so long and he was much blonder when he was younger. I considered him blond on Days but it was dark blond. Now his hair is much darker and if he were to just now appear on the scene I suspect people would call it brown. Even the show goes for brownish in younger versions of Dean. But it is hard to discard the mental image of the blond kid (or at least blond highlights).

You know he was once a lot blonder, though, because his beard comes in reddish.

Beard red definitely. Still don't see the blond, not even dark blond. I think maybe this comes down to personal definitions of blond. It's like the "is it blueish-green or greenish-blue?" debates I've had with friends. Teal is a very subjective color. Apparently so is blond and hazel.

ETA: I first saw Jensen as Alec. Alec was also a brunette.

if he were to just now appear on the scene I suspect people would call it brown

I suspect that too.

But they did cast his earliest incarnation blond, even though they could have gotten away with it for longer.

Jared's sister described his eyes as "blue-brown," and depending on the light and what he's wearing, I've seen film and photos of his eyes both very dark and really light, and in some of the stills, they did look blue.

JA's contacts may have been tinted to give him that jewel-green shade. Since his surgery his eyes have appeared a much more gold-grey-green hazel.

I've seen off-season photos where his beard looks reddish. H's beard was the same way, and his hair appeared brown in most lights, but as Plei suggested, matching it to hair color put it in the dark, "dirty" blond range.

I think Misha's a master at getting what he wants from the fanbase. He's as much a student as an object on display; his level of actual engagement is difficult to determine.

I ignore Clif, as long as he does his bodyguard job and keeps my pretties safe.

[link] Huh. Jensen is even brown here with blond highlights. I dunno. Just the mental image he projects. ?

I first saw Jensen as Alec. Alec was also a brunette.

Ben and Alec are totally blond.

Ben and Alec are totally blond.

Oh wow. Okay.

Oh wow. Okay.

Dark blond, mind you. But less ambiguously blond than Dean.

Does it really matter?

Runs away

More than getting hair and eye colour wrong or wrongish, it's the getting body-types wrong that bothers me. Like Castiel being taller than Dean or a character having a better (or worse) body than they actually have.

I agree with Perkins that it doesn't matter much, but sometimes the details being off jars me when reading fic, or pulls me completely out. Castiel does not weigh 98 pounds.