I have heard recently from a friend that a few of the light malt extracts out there use some adjuncts, to help keep the color light. Which to me would impart a big flavvor diference. Not being as much malt and all. I was told (and it makes no sense to me either, but I belive the source) that for some reason malts are not treated the same as other food items, in tha tthey do not have to list ingredients and nutritional values. Not sure why, but I have never been able to find it anywhere. Not sure how acurate all this is but like i said it comes from a reputable source.
Amber will have some caramel in it. Gold will have more body than light, but the flavor will be about the same. If you are making a Pilsner, go for the Gold.