Okay, fair warning, most men will find this utterly boring so tune this post out, 'kay?
This is how I (and the world of cosmetology) define blonde: Sit out in the sun for hours on end with wet hair, ideally using a little straight lemon juice to speed up the process. What color is the palest your hair gets naturally? Mine will turn platinum. Brunettes end up with reds or orange. Now that I'm an old bag I use medium ash blonde to cover the grey, does a nice natural looking job. In my younger days I used to buy Dark Ash Blonde. Sounds much classier than what my mother used to call it -- dishwater blonde. A fact of life is that as we age our natural pigmentation begins to fade, which is why women who don't change their dye jobs or makeup palettes after a certain age look foolish.
Really it's about the base tone -- Understand the undertones of your skin and hair is key to understanding what color family to work from when it comes to makeup and hair color. Accepting that you can't use screaming whore scarlet after a certain age is the difference between being a pathetic old woman and a cougar. Understanding that you have yellow undertones in your skin narrows the color families you choose from. Coordinating that shit with your hair color is the difference between having a half assed look and looking put together without a lot of effort.
And yeah, there was a time I wanted to go into either art or hair and makeup which is why I eve know half this shit
/end chick rant