Replacing background around hair tutorial question

[Control Z]

I took some quick headshots against an imperfect background and would like to make it a solid white (or any color, really).  (I had a flash on the background and had hoped to blow it out to pure white, but only the bottom got overexposed.)  I followed the instructions in the tutorial, but it's not coming out perfectly.  (Tutorial: http://www.damiensymonds.net/replace-background-hair)

The photo with the whitish background is the before image, the one with the yellow background is the after.  I didn't choose yellow for any particular reason.  I just added a new layer and filled it with a color.  

As you can see, the hair has a yellowish tinge.  Is there something I'm doing incorrectly?  When I fill the yellow layers with white, it looks basically fine, but any color other than white shows through.  

Is there an easier way to make the background uniform?  

Thank you.

[Damien Symonds]

So far so good.  Now return to the Levels 1 layer and mask as needed.

[Control Z]

30 minutes ago, Damien Symonds said:

So far so good.  Now return to the Levels 1 layer and mask as needed.

Right, but when I paint black over the hair, the original white background shows through the spaces in the hair.  I don't understand how to separate the hair from the color without detailed selection.

Edited May 15, 2016 by Control Z

[Damien Symonds]

No, its quite ok for some of the hair to be yellow.  That's how it would be if you really had shot her in front of a bright yellow wall.

[Control Z]

OK, I'll play around with it; thanks.  

At some point, would you be able to go through your thinking on how you figured out this process?  For instance choosing the multiply layer?

[Damien Symonds]

THIS is what you need to mask:

The very distinct obvious line.

[Control Z]

1 minute ago, Damien Symonds said:

THIS is what you need to mask:

The very distinct obvious line.

So mask between the red line and just outside the hair?

[Damien Symonds]

No, just inside the hair.  You MUST let some yellow bleed into the hair.

But you have to mask with a nice big soft brush.   To make it subtle and gradual and plausible.

[Control Z]

And how to handle the patches of white inside the hair curls just above the right shoulder?

[Damien Symonds]

What?  Paint white on those areas of the mask, of course, to fill them in with yellow.

I'm not sure what you don't understand, exactly?

[Control Z]

I guess what I'm asking is that if you have to carefully mask the hair, how this is easier than carefully selecting the background?

[Damien Symonds]

No, you DON'T carefully mask.  You use a big soft brush.

[Control Z]

Thanks, I will work on it.  

I know you'll probably freak, but another quick and easy, though admittedly imperfect, method to get the background to white is to use a combo of adjustment brushes and gradient adjustments in ACR or Lightroom, with the exposure slider cranked all the way up, with the Auto Mask box checked, so it avoids the hair.  

[Samantha LaRue]

12 minutes ago, Control Z said:

Thanks, I will work on it.  

I know you'll probably freak, but another quick and easy, though admittedly imperfect, method to get the background to white is to use a combo of adjustment brushes and gradient adjustments in ACR or Lightroom, with the exposure slider cranked all the way up, with the Auto Mask box checked, so it avoids the hair.  

adjustment brushes and auto mask are probably 2 of the features Damien hates the most.

[Control Z]

Just now, Samantha LaRue said:

adjustment brushes and auto mask are probably 2 of the features Damien hates the most.

Well good thing he's on another continent!