Enzymes in light colored fruits such as apples, pears and peaches can cause oxidative browning as soon as the fruit is peeled or cut. Browning can cause loss of vitamin C. Because fruits are usually served raw they are not usually blanched to prevent this discoloration. Instead, chemical compounds are used to control enzymes in these fruits. The most common treatment is ascorbic acid (vitamin C). Ascorbic acid may be used in its pure form or in commercial mixtures of ascorbic acid and other compounds. Browning can also be halted temporarily by placing fruit in citric acid or lemon juice solutions or in sugar syrup. However, these measures are not as effective as treatment with ascorbic acid in its pure form. Apples, as well as other fruits, retain better texture and flavor if packed in sugar or sugar syrup. However, sugar is not necessary to safely preserve fruit. Fruits packed in syrup are generally best used for uncooked desserts, those packed in syrup or unsweetened are best for most cooking purposes, because there is less liquid in the product.http://www.urbanext.uiuc.edu/apples/preserving.html
I did treat 'em! And the jam turned out just fine...a beautiful rose tint.
I think this is just the way they're supposed to be...my apple butter I buy in the store is brown too, come to think of it. I guess brown peach butter is to be expected. Never had peach butter before though...