A question about a recipe: Pear Pineapple Ginger Jam

Before you substitute brown sugar for white you need to be aware that brown sugar is really white sugar with molasses (which may come from sugar beet) added to give it colour and texture and appear to be more healthy. Moscovado sugar is darker natural brown sugar as is demerara. The added molasses in the brown sugar or the different taste of moscovado and demerara sugars may alter the taste of your jam. Alternately you can use honey or corn syrup as a sweetener if you wish not to use white sugar.

I personally haven't done it (yet) but I don't see why you wouldn't be able to. A good thing to keep in mind though would be that brown sugar has a higher moisture content than regular sugar and thus weighs more per given volume. I c regular sugar probably weighs as much as about 3/4c brown sugar ( only an approximation). Depending on how wide of a margin a particular jam recipe gives you (some use a lot of sugar, some call for adding pectin ) you may end up with a slightly runnier jam, which isn't necessarily a bad thing.