Rye breads naturally tend to have a dark colour, especially if they are of a higher extraction flour. However, I've seen alot of rye bread formulae that add various ingredients to produce a dark or black colour to the bread crumb. These ingredients include; molasses, dark malt extract, dark or medium trumalt, etc. Since this forum is for the 'artisan' I thought I'd include a bit about the artisan method to increase the dark or black colour of rye bread.
Firstly, the colour is achieved by method rather than adding an ingredient that imparts 'colour'. Surprisingly, or not, depending on your point of view, the artisan method improves the food value of the product also.
The dark colour is achieved by allowing the amylase activity of the flour or meal to degrade a significant portion of the starch present in the flour or meal to produce simpler sugars called 'maltose'. This is done by stimulating the amylase enzymes by soaking a portion of the grain, meal or flour to be used for the bread in water, and allow it to stand for a predetermined time at a predetermined temp. This 'soaker' is then added to the dough as one would add any other portion of the flour.
Typically, 15-30% of the total meal or flour is soaked to achieve maltose development. Of course, this depends on the type of flour or meal used, the colour intensity desired in the finished loaf.
Finally, the baking method for this bread has the finishing effect, caramelising those sugars to produce that desired 'dark' or 'black' colour. The baking time is extended significantly for a couple of reasons; to stabilise the crumb by reducing the moisture content which is very high as the degradation of starch into maltose liberates water that needs to be baked off. Secondly, an increased baking time ensures sufficient maltose quantity is caramelised to a sufficient degree to achieve the dark colour desired.
See this formula below as an example of using the soaker method.
I'll make some of these next week and post a few photos.