When it comes to color-change gems, there are few choices to be made.  Best-known and most popular by far among these phenomenon stones is alexandrite—a green-to-red chrysoberyl with a hardness of 8.5 that is found in Russia, Sri Lanka, and Brazil.  Prices for the best stones are generally five and six figures.

Next in supply and stature among the slim ranks of color-change gems is blue to purple sapphire, which caught on with both collectors and designers after discoveries of deposits in Tanzania in the 1960s and Sri Lanka even earlier.

Third, but a viable candidate to leapfrog over sapphire in status, comes color-change garnet.  A recent find in Kenya has given the world its first true-blue garnet—admittedly only in fluorescent light.  But when it comes to garnet, half a blue is better than none.

Fourth in the color-change rankings—both in production and prestige—is spinel.  Granted, sizes tend to be less than 1 carat, but its hardness, which is 8, is a plus.  Nevertheless, the real appeal is aesthetic.

For me, spinel has a distinctive color change that only superficially resembles that of color-change sapphire.  It flips from a steely Hope Diamond blue to a subtle violetish-purple that bears a strong resemblance to some of the rarest and most dramatic of all monochrome spinel hues—in this case, blues from Sri Lanka and lavenders from Vietnam.

Given the patience-straining availability of both blue and violet in normal spinel, the case for ownership of the frustratingly few specimens of the color-change variety is as potent as any that can be made for a color-change gem. At the risk of further aggravating the collectors we talked to, it seems irresponsible not to state the plain truth about color-change spinel: It is a true treasure and a true bargain.  This fact begs another truth: The days of under-pricing this two-toned gem are about to end.