The region of chromatin that is stained lightly is

In a typical nucleus, some regions of chromatin are loosely packed (and stains light) and are referred to as euchromatin. The chromatin that is more densely packed and stains dark is called heterochromatin. Euchromatin is said to be transcriptionally active chromatin, whereas heterochromatin is inactive. The centromere is mainly composed of heterochromatin.