The sky-blue glaze is a kind of precious monochrome glaze in ancient China. It was generally believed to have originated from the legendary Chai kiln, but up to now, the earliest sample appeared at Ru kiln. Therefore, some scholars believe that the sky-blue glaze is a unique product of Chai and Ru kilns before the Southern Song Dynasty. However, in recent years, other scholars pointed out that the sky-blue glaze is not the “patent” of Chai and Ru kilns, and that the earliest sky-blue glaze might have originated from Yaozhou kiln in the Five Dynasties. In this work, we first classified the so-called sky-blue glaze samples from Ru kiln in the Northern Song Dynasty and from the second stage of Yaozhou kiln in the Five Dynasties according to the experience in cultural relics. We then measured and compared their chromaticity values, in order to discuss the provenance and origination time of the sky-blue glaze.