Both the Portuguese and the French held some territory in India, while the British dominated the rest of it. Both of the lesser colonial powers in India issued stamps which are, for the most part, neglected by Indian collectors, and which have potential multiple market appeal in India, their home countries, and among collectors of European colonies. Interestingly, the Portuguese held out the longest of the three, and issued stamps for their colony until India seized it in 1961, ending the occupation. It's not the only time that obsolescent imperial visions of grandeur have benefited philatelists.
In 1952, Portuguese India issued two souvenir sheets and a strip of two + label to celebrate its first stamp exhibition (Scott #522-23, 523a). The souvenir sheets picture St. Francis Xavier and his tomb, while the strip contains a one stamp picturing the saint and another picturing Portuguese India's first stamp. 30,000 of each were issued and Scott '14 prices the sheets and the strip unused at $29.00 and $25.00 respectively.
These items have additional market appeal among collectors of India, Portuguese Colonies, and collectors of Religion and Stamp-on-Stamp topicals.
Those interested in learning about investing in stamps should read the Guide to Philatelic Investing ($5), available on Kindle and easily accessible from any computer.