Midwestfarmboy,
You can do hightlights in synthetic hair. But there is one caveat: the factory will not use more that 25% of synthetic hair in a unit. The reason is that synthetic hair above that percentage does not blend well with real human Remi hair. You can use synthetic is smaller amounts for gray and highlights but when it gets above 25% the difference becomes noticeable. Synthetic hair does not reflect sunlight like real human hair and when the wind musses up your hair the synthetic reacts differently and it looks fake. Small amounts are fine--25% and above is a no-no.
Regards,
John
http://toplace.com/