I am new to making bread, and have made a number of loaves using King Arthur bread flour, salt, water and a sourdough starter. The bread tastes great, but when I toast it I am never able to get the crumb to turn brown and crispy, no matter how long I toast it for. What could be going wrong? (The toaster works fine by the way...)

Here's a shot of a recent, representative loaf:

http://oldwithoutmoney.com/sourdoughLoafnBuns.jpg

A some significant cracking along one end & side, but reasonable form, decent results from scoring, a decent crust, and it tasted yummy good.
(Baked in a loaf pan at 425.)

But none of that brown caramelizing that characterized many a fine loaf.

What can I do to get that nice brown color? 

Thanks