Seems to be brown leather with a touch of decoration (possibly sea shells?), if this pic is reliable:
Edit: I have no other information about these things. I managed to stumble upon this pic, but it had no context other than 'Infantryman of the Kingdom of Dahomey during the Franco-Dahomey Wars in the 1890s.'
European covers of this sort were sometimes made of leather, so it seems reasonable they'd use similar materials in Africa. That's all I have.
Must say, I love that one fellow's fish hat. I want one.