The blue one's the only one with straight hair (duh). Note that the hair's falling straight down, it doesn't go like the bad example to the right. The silouette of her hair (blue) suggests that it's straight hair, but the strands (orange) don't fall down; instead, they go everywhere. The example on the right doesn't make sense as far as hair goes; if the hair's straight, you gotta show that it's going down by drawing the strands that way.

  On the left are two different correction of the above right picture. The further left one has *the* straight hair; see how the strands are going down? The other picture also shows what could be defined as straight hair, but in this tutorial, we'll call it spikey.

  The bottom line: strands always follow the silouette of the hair. For example, in the pictures above, the orange lines should go in the same direction as the blue lines. This also means that when you're coloring hair, highlights also follow the silouette of the hair just like strands. Try drawing long strands first, then putting the highlights over the strands; that way, it's easier to tell whether your highlight is correct or not. ^_^ Look how the highlights follow the strands in the picture to the right!

You might say "Duh, I know that," but I see people making mistakes on it all the times... So I provided an example of the mistakes: click here!