The work aims to research the reasons and influencing factors of oxidized color on the surface of cold-rolled strip under full-hydrogen bell-type annealing, which could provide theoretical basis and practical guidance for optimizing the full-hydrogen bell-type annealing process and reducing the surface oxidation color of strip steel in actual production. The effect of the experimental steel composition and annealing temperature on its surface oxidation color was studied through a full-hydrogen bell-type annealing furnace. X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were used to characterize the composition and micro-morphology of oxidized color on the surface of the experimental steels. After annealing, there were a large number of oxide particles with a diameter of about 100~300 nm attaching to the surface of the experimental steels with oxidized color. And the particles were mainly composed of Mn2O3, MnO and SiO2/SiOx, etc. These particles made the surface of the experimental steels appear light blue from the macroscopic view. As the annealing temperature increased from 570 ℃ to 585 ℃, the proportion of 36Mn and 50Mn steel coils that produce oxidized color increased from 1.69% and 21.9% to 6.27% and 53.1% respectively. 17Mn and 25Mn steel coils did not produce oxidation color when annealing between 570 ℃ and 585 ℃. And when the annealing temperature was increased to 660 ℃, all steel coils produced oxidation color. The main reason for oxidized color production is the surface segregation and selective oxidation of alloy elements during the annealing process of the strip steel. The Fe element is not oxidized during the annealing process. Annealing temperature and the content of Mn have a significant effect on the production of oxidized color. The higher the annealing temperature and the content of Mn are, the more likely the experimental steels will produce oxidized color.