This is going to sound CRAZY but...
 

White mage and fighter to me seem very similar. They both have red hair and similaritys about them so I was thinking?... what if there brother and SISTER! this is crazy I know but with the plot twists Brian can bring in who knows what might happen?

could happen.

but it does seem very crazy.

i'm still waiting for fighter to hook up with EPS.

White Mage and Fighter brother and sister? NAW! I mean common, Black Belt and Red Mage could be bro and sis, and of course there is the painful love triangle between Thief, Black Mage, and Garland, but Fighter and White Mage? What the heck are you thinking man?!?!?!

Sarda, Left Hand Man Gary, Red Mage, and Red Mage's dad are all cousins because they have white hair.

Please, everybody knows the real sexual tension is between Red Mage, Thief and Drizz'l.

other similarities between fighter and whitemage, in the sake of openmindedness, other then the color of light reflected by there hair that come to mind are the following:
a shared fight for goodness
a fondness for food (italian/edible)
unbreakable bonds to blackmage (stalking/friendship/abuse/omniloathe)
an afiliation for questing

oh, and competence, they are both (sometimes surprisingly so) useful.

Of course, because everyone is related to everyone else who is even remotely similar to themselves.

wait! was that sarcasm? are you saying that people that look similar aren't actually related!? Damn! then i'm NOT related to Brad Pitt *cries*

Whm would kill Fighter the instant she found out, "I am NOT related to an idiot! What if we share the same idiot genes?! OH MY GOD! DIE DIE DIE!!" *Pulls out hammer of idiot doom.*

I've always suspected Sara was adopted. I actually think what happened is that when the Devine Deity saw that the most stupidest (He's so stupid, you have to use bad grammar to show how mind boggingly idiotic the guy is) man was the king of stupid, yet powerful kingdom, He put it upon himself that the man wouldn't have any heirs.

With a rusty pair of scissors.

So, one day His wife, The Queen, decided she wanted a kid. So she simply went over to the local orphanage and adopted a baby, and told Steve she had a baby. Steve commented on how it had his eyes, hair, looks, gender, and mumbled on about how King String from the fictional nearby country Stringtopia had gotten a new car.

He then went off to work on his greatest invention, Robo Steve, intending to send it back in time before King String would ever become a threat to King Steve's upcoming elections.
-------------------- /Rant

Btw, maybe they're all white haired because they are probably all Half-elves?

As for Fighter and White Mage, They are both a rarity in a world of evil idiots, so therefore they have a rare haircolor.