appearance of more silicate dust in the cooling brown dwarf atmospheres. Yet the cooler T-type brown dwarfs, like Gliese 229B, have blue colors in $J-K$ (e.g., Leggett et al. 1999; Tsvetanov et al. 2000). The spectra and colors of these cool brown dwarfs can only be fit by atmosphere models that assume the silicate dust has settled below the visible atmosphere (e.g., Allard et al. 1996; Marley et al. 1996; Tsuji et al. 1996). Models in which the dust does not settle (Chabrier et al. 2000) produce T-dwarf colors that are at least 2 to 3 magnitudes redder than observed. Marley (2000) has demonstrated that a simple model in which all clouds are a single scale-height thick can explain this behavior, but the assumed distribution was prescribed rather than being calculated from any model physics. Correct modeling of the atmospheres of cooling brown dwarfs and the ultimate assignment of an effective temperature scale to the L-dwarf spectral sequence (e.g., Kirkpatrick et al. 1999; Basri et al. 2000) requires a characterization of clouds. The ideal model would have a small number of free parameters, predict the vertical distribution and particle sizes of the condensates, and yet be simple enough to be 