We present three-band simultaneous observations of a weak-line T-Tauri star, CVSO 30 (PTFO 8-8695), which is one of the youngest objects having a candidate transiting planet. The data were obtained with the Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT) on the 188 cm telescope at Okayama Astrophysical Observatory in Japan. We observed the fading event in the $$g^{\prime }_2$$-, $$r^{\prime }_2$$-, and zs, 2-bands simultaneously. As a result, we find a significant wavelength dependence of fading depths of about 3.1%, 1.7%, and 1.0% for the three bands. A cloudless H/He-dominant atmosphere of a hot Jupiter cannot explain this large wavelength dependence. Additionally, we rule out a scenario with the occultation of the gravity-darkened host star. Thus our result is in favor of the fading origin as a circumstellar dust clump or occultation of an accretion hotspot.

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