The question asks for the one event that falls outside the 1980s, so each option has to be dated.

Separation of Doordarshan from Aakashwani took place on 1 April 1976, when television was delinked from All India Radio and constituted as a separate service under the Ministry of Information and Broadcasting. That is the mid-1970s, not the 1980s, which is why it is the event that did not occur in that decade.

Television becoming colour belongs to 1982. Colour transmission was introduced for the Independence Day broadcast and then for the Asian Games held in Delhi that November, which is the event usually credited with pushing colour sets into Indian homes.

Rapid spread of the television network across India is squarely a 1980s development. The low-power transmitter programme of that decade extended coverage from a handful of cities to a large majority of the population, and the INSAT satellite series carried the signal nationwide.

Ramayan was launched in 1987 and Mahabharat in 1988 — the serials that drew the era's largest audiences and confirmed Doordarshan's national reach.

Hence the event that did not take place in the decade of 1980 is the separation of Doordarshan from Aakashwani.