Brown (With Copper Streaks) Hair

Today's topic is CHARACTER DESCRIPTION because I feel like analyzing this relic of the past until doomsday.

You may have noticed in yesterday's excerpt that I was into hair color. Yeah, and I was also into age. And since this was a fantasy, each main character had a horse. Each horse was a different color, and each horse had a name.

     "'She fell off Sirlan, Evran's bay stallion, you know.'
     "'I know what Everan's horse looks like, Calanor,' Lisson snapped. She turned the four-year-old girl onto her back and felt her pulse. 'She's still alive,' she murmured, brushing Kirian's brown (with copper streaks) hair away from her sweaty face." [sic]

It's a big deal in middle-grade novel, I think, which was more or less what I was reading when I wrote this. But as I've grown older, I've come to grit my teeth when the first page of a novel looks something like,

     "'My turn to answer the phone this time!' insisted Peter. He was smaller than his twelve-year-old twin sister, but they both had the same deep blue eyes, medium blond hair, and lanky build. He did his best to beat her to the phone, scrambling over a kitchen chair.
     "'Don't bother, little brother.' Elise was already two steps ahead. She scooped up the receiver, flipped her shoulder-length hair, and smiled sweetly in his direction." - A Light in the Castle, by Robert Elmer, which is, according to the AR BookFinder, for Middle Grades 4-8. (These paragraphs really are on the first page. Don't get me wrong - I love this book. It just happened to be nearby.)

Now when I write, I try to let a few pages (or chapters) go by before I mention any specific physical description (unless it's vital to the story). I hope that the person behind the body becomes more identifiable than the hair color. There's a danger to this, though. Readers can get upset when they have one picture in their head and have to change it. (I was upset when I discovered Meggie had curls - red curls? - in Inkspell.)

So what do you do? What age level are you writing for, and do you describe your characters right away? Does the age level have anything to do with it? Or do you wait 'til later in the book? Or do you never tell the reader how the character looks? Any tricks that you use, such as giving appearances away through dialogue instead of description (which is what I try to do but don't always succeed at) or the thought process of another character? (And has that thought process trick become cliche?)