Colony is the least metamorphosed CO chondrite (CO3.0). However, it is badly weathered. In order to show both primary and secondary features of the matrix and discuss the effects of terrestrial weathering on the matrix mineralogy of Colony, we performed combined SEM, EPMA, CL, and TEM studies on this meteorite. EPMA data of the matrix of Colony show that matrix composition was changed by terrestrial weathering. The matrix composition can be represented by three hypothetical components : an Fe-rich component (Fe hydroxide-rich weathering products), a component with olivine-like composition, and an Fe-poor, Si-rich component. TEM observation reveals that the matrix contains abundant Fe-rich poorly crystalline interstitial materials, abundant ferroan olivine (Fa_<50>-Fa_<60>), less abundant magnesian low-Ca pyroxene (En_<99-90>), magnetite, and minor amounts of spinel group minerals, troilite, and rare Ca-rich pyroxene. Among these phases, anhydrous minerals are primary minerals. The Fe-rich component estimated from EPMA data is composed of abundant Fe-enriched, nearly amorphous material, minute phyllosilicates (mainly saponite, serpentine, and minor amounts of chlorite and montomorillonite), and goethite. The Fe-poor, Si-rich component estimated from EPMA data is also composed of basically the same but seems to contain more phyllosilicates than the Fe-rich one. Matrix olivine crystals often contain planar defects parallel to (001). Such planar defects were probably formed in the initial stage of iddingsite formation by terrestrial weathering.