Malgudi Express: From the pages of RK Narayan to the railway tracks of Mysore. - Vageesh

It was actually Kerala-Karanataka express at the time this movie was shot , not just Karnataka express. :)
I believe this sequence was shot just months before KK was split into separate Kerala and Karnataka expresses ( The split was from October, 1982, while this movie was shot just before that).
The livery was changed in the 90's to the Rajdhani livery. TN, AP and Kerala expresses too had their own set of liveries that kept on changing.
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The last one is also just a few empty coaches of the KK's rake being shunted around for the song. Brindavan's rake was pure green with yellow stripes above and below the windows.
(Observe that all the trains in the film characters are boarding are actually empty rakes with random crew being moved to the yard at the MYS end of the SBC station and the final scenes happen on the present day PF2/3).