We report the structure and dynamics of concentrated biphasic mixtures comprised of distinct populations of attractive and repulsive silica microspheres by means of confocal laser scanning microscopy. One population of colloids is rendered hydrophobic by chemically modifying their surface. These species flocculate when suspended in an index-matching (water-DMSO) solvent, while their unmodified (charge-stabilized) counterparts remain individually dispersed. By labeling the two populations with different fluorescent dyes, we can image the two phases simultaneously and independently. We investigate the mixture's structural and dynamical properties at constant total colloid volume fraction and different ratios of the two phases. Specifically, the effect of the excluded volume of stable particles on the gel microstructure, and the effect of the arrested gel network on the dynamics of stable particles are discussed. These results will facilitate the development of concentrated colloidal inks for direct-write assembly of complex 3D structures. Moreover, they may provide new insights into the complex dynamics of supercooled colloidal liquids near confinements.