The thermal spectrum of the infrared and optical emission from an accretion disk around a compact object has been calculated, assuming an optically thick, finite disk and a power-law dependence of disk temperature on radius. This calculated spectrum is then compared to the spectrum of blackbody radiators whose temperatures and radii are equivalent to B0 and O5 stars. For likely values of central disk temperature and maximum radius, the disk emission can dominate over the emitted spectrum of the companion star in a binary system. This occurs because the frequency dependence of the star's emission in the Rayleigh-Jeans limit (Sv is proportional to v-squared) falls off more rapidly with decreasing frequency than the emission from the disk. As illustrative examples, the consequences of these results for three black hole candidate systems (Cygnus X-1, Circinus X-1, and GX 339-4) are discussed. If not correctly understood the contribution of significant infrared and optical disk emission to the spectrum of the primary star can lead to serious errors in estimating the parameters of the binary system. Possible methods for determining the relative contributions from disk and star in binary systems are discussed.