Grey goo is a common-or-garden science-fiction apocalypse, runaway nanomachines converting all available mass into more copies of themselves until there’s nothing less but a seething sea of nanotech, some waiting, and hyper-accelerated evolution as cosmic radiation and copying errors start the survival of the fittest all over again. But what about the other kinds of catastrophic goo?

• Brown goo: nanomachines designed to turn everything into chocolate after a nanogineer has a particularly bad breakup.
• Rainbow goo: a commercial grade decorating can of self-paint malfunctions, losing its limiters and attempting to celebrate the entire planet.
• Green goo: rogue reforestation extremists program bots to turn everything into moss and seeds.
• Marble creep: artistic terrorists attempt to restructure the world as a renaissance testament to capitalistic greed. Irony makes a special appearance to set it off in their own headquarters. Cauterizing the live artistic elements, the government publicly displays it as piece on hubris. Whether they’re aware of even more irony in doing so is the subject of several PhD theses.
• Stu gu: a lonely nanogineer programs nanobots to replicate him from anything they can find. The resulting race of Stus could have been a serious socio-ethical problem, except they couldn’t stand each other, and spread out to get nanogineering contract positions based on the most effective viral brand expansion of all time.
• New goo: nanobots specifically designed to vary their design with every iteration. Standard response to detection is a fusion warhead, hence their informal nickname, “instant glass”.
• Antisinister: a nuisance bot designed to convert left socks into harmless vapour (they identify the sock chirality by analyzing sweat and stress patterns in the fibres). Von Neumann agencies are showing increased interest as the bot is believed to have infiltrated temporal research stations.