Could you clarify your question? We may be able to be more helpful if you could do so. Are you asking if longer baking reduces gluten? Are you asking if darker flours in general reduce gluten? Barley, rye, spelt, triticale and of course wheat, all contain gluten, a protein that contributes elasticity to dough. Longer baking does not reduce gluten (if that's what you're asking). Some flours are higher in gluten than others. With regard to white flour milled from wheat, bread flour contains a greater amount of gluten than All Purpose. Cake flour contains the least amount of the three. Hope that helps.
I'm not sure there is a straightforward relationship between crust color and gluten content, unless the crust color gives you a hint as to the types of flour the roll is made of (a roll heavy in rye would be darker than white wheat or even whole-wheat, and rye is lower in gluten than wheat). What exactly are you trying to determine ?
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