The first post card that I sent was to Germany and it was the yellow post card. I put additional stamps on it. And it had reached.
That said, it is meant for sending within India only. Additional stamps not requires.
Other cards require stamps - Rs 6 for within India, Rs 10 for Pakistan, SriLanka, Bangladesh, Nepal, Bhutan, and Rs 15 for the rest of the world
For sending in envelope, the prices are different and higher
Hope it helps.