Specific and tunable modification to the optical properties of single-wall carbon nanotubes is demonstrated through the direct encapsulation into the nanotube interior of guest molecules with measured static dielectric constants. Optical measurements on SWCNT populations containing over thirty distinct simple compounds of varying static dielectric from 1.8 to 109 in large diameter nanotubes, and 15 compounds in small diameter nanotubes demonstrate for the first time experimentally the general effect of filler static dielectric on the nanotube optical properties. Comparison to effective medium theory predictions is presented, and guest molecules are identified that lead to effects disobeying the general trend and theory. These results both demonstrate a new degree of exploitable modulation in the optical properties of SWCNTs, and provide a foundation for examining higher order effects in host-guest interactions in well controlled pore size materials.