We experimentally observe the formation of spatial dark gap solitons in higher bands in one-dimensional waveguide arrays possessing a saturable defocusing nonlinearity. By using the prism-coupler scheme, pure Floquet-Bloch modes of higher bands are excited and dark gap solitons are formed due to the counteraction of normal diffraction and the defocusing nature of the photovoltaic nonlinearity. The modulation of refractive index induced by the soliton formation is demonstrated by the guidance of a low-power probe beam in the waveguide array sample. Additionally, the phase structure of dark solitons formed in the second band is discussed.