In general, implying that a gemstone purchase is a money-generating investment is fraudulent. There are good reasons for this. One is that in order to recoup your initial "investment," let alone make additional money, you have to have a buyer or buyers ready to purchase the item. Finding these buyers is harder than it seems. Remember that if you walked into a store, stumbled onto a website, or purchased a gemstone from a shopping channel, then anyone else in the general public can do the exact same thing. This leaves absolutely no reason for anyone to pay you more for the same item.
Another point in "investing" is that you need to have full knowledge of what you are putting your money in. You wouldn't invest in real estate or buy stock without some understanding of how those markets work-so don't do it with gems. How does the market work for gems? How do you market them? What are the legalities involved with selling a gemstone? What does the collector market require in a gem? Do you know the background of the person selling the gem? Are you sure that the source is legal and legitimate? And most importantly, do you know how to access the quality, identity, and origin of the gem that you are buying? If you can't answer these questions about the gem you are buying, then you are obviously treading on very shaky ground. In fact, you will be very lucky if you get more than half of your money back.
Colored stones, in particular, have very unstable markets. Most are mined in third-world countries with unstable political situations and limited infrastructure. A now reliable source may be inaccessible in a few months due to a civil war in the area. The United States may enact a boycott on the source nation due to human rights violations - like that on Myanmar/Burma right now. A gem can lose value due to scandal in the mass media-like emerald in the nineties when the common practice of filling fractures was exposed on national television. Tanzanite took a severe blow to its value when it was falsely reported to be a fundraiser for Al Qaeda in the Wall Street Journal. A stone that is found in only one place today may be found in several more places in the next year. A stone that is rare may not have enough public recognition to achieve high prices in the market. All in all, colored stones are not predictable investments, and just because a stone is a "Cuprian tourmaline," for example, it is not necessarily a high-quality "Cuprian tourmaline."
So here are some of the "investment" scenarios that we have seen.