Yes! Maybe? Red-orange!
Conventional wisdom says that synesthesia is innate -- you're either born with the condition or you're not, end of story. If you happen not to have been born that way but would really, really love to experience numbers as colors, or colors as sound ... then you, my sense-straight friend, are pretty much out of luck.
Except ... maybe not? A group of psychologists at the University of Amsterdam have been testing whether synesthesia might, actually, be learned. Synesthetes' innate cognitive wiring leads them to augment their perception of the physical world; the researchers wanted to see whether the reverse could take place -- whether an augmented physical world could lead to synesthetic perceptions in people who weren't born with "crossed senses." And the researchers have now published their findings in the journal PLoS One.
Those findings, it should be said, are fairly inconclusive, but they also offer some hope -- some colorful, fragrant hope! -- to the wannabe synesthetes of the world. The Dutch scientists' attempt at synesthesia-in-reverse is the first experiment of its kind, and it might well lead to more research into the intriguing realm of willful sense-crossing.