釋氏要覽 1.86

1.86

此從衣色名之也。僧史略云。問緇衣者色何狀貌。答紫。而淺黑。考功記云。三入為纁。五入為緅。七入為緇矣固知緇本出絳雀頭色。即紫赤色也。故梁淨秀尼見聖眾衣。如桑熟椹。此乃淺赤深黑色也。

This is named after the color of the robes. The Sengshilüe states: "Question: What does the color of the black robes (zīyī) look like? Answer: Purple, yet light black. The Kaogongji states: 'Dipping three times makes it light red (xūn); dipping five times makes it dark red (zōu); dipping seven times makes it zī (blackish).' Thus we know that zī originally derives from crimson bird-head color, which is a reddish purple. Therefore, when the nun Jingxiu of the Liang saw the robes of the noble assembly, they were like ripe mulberries. This is a light reddish deep black."