colorless

Hydrogen sulfide is a colorless, flammable, highly toxic gas with the odor of rotten eggs.

Trichloroethylene, or TCE, is a colorless liquid that has been used to remove gunk from jet engines, strip paint and remove stains from shirts dropped off at the dry cleaners.

The gas is colorless and odorless.

In demonstrations, Xu's MOF electrochromic film took 2 seconds to switch from colorless to green with an electric potential of 0.8 volts, and 2 seconds to switch to dark red with 1.6 V. The film maintained the green or red color for 40 hours when the potential dropped, unless a reverse voltage was applied to return the film to its transparent state.

As oxymorons go, it’s the operatic equivalent to Noam Chomsky’s famous syntactic puzzle “Colorless green ideas sleep furiously.”