This is a special term used by Patañjali (200 B. C.) in his celebrated work the Yogasūtras (4.7). Normally the karma of individuals that fructify in this life or in the future lives is classified either as ‘śukla’ (‘white;’ i.e., puṇya or meritorious) or as ‘kṛṣṇa’ (‘black;’ i.e., pāpa or sinful). The former bring good results whereas the latter cause evil effects. But the karmas done by a perfected yogin are neither kṛṣṇa nor śukla, since he never commits sins; and offers the fruits of all his meritorious deeds to Īśvara or God. Hence his karma is known as ‘aśukla-akṛṣṇa,’ ‘neither white nor black’ and does not produce any result that will bind him in any way.
See also KARMA.