Epidermal layer and muscle wall of colon?
Good question. The colon is lined by epithelial cells (as are all hollow organs). These particular epithelial cells are different from epidermal cells, which are another particular type of epithelial cells found in skin.

Epithelial cells are distinguished by the way they connect with each other using tight junctions to form a permeability layer between compartments. 


In the colon, the purpose of the epithelial cells is to both to absorb water and to form a barrier between the luminal contents and the body.  They form the layer facing the lumen. The muscular layers of the colon, both the circular and the longitudinal, are further out from the lumen. You can see them in this histology slide: