It looks like researchers from Purdue just got a lot closer to matching the power of Vantablack on the other end of the luminance spectrum.
"The new paint contains a compound called barium sulfate, which is also used to make photo paper and cosmetics.
“We used a very high concentration of the compound particles,” explained Prof Ruan. “And we use lots of different sizes of particles, because sunlight has different colours at the different wavelength.” -BBC News
How much each particle scatters light depends on its size, "so we deliberately used different particle sizes to scatter each wavelength".
“In a study published Thursday in ACS Applied Materials & Interfaces, researchers at Purdue University say they’ve now made the whitest paint on the planet. In creating the whitest paint ever, which researchers say reflects up to 98.1% of light, the Purdue researchers are outdoing their own record, set just last fall, when they developed a paint that reflects 95.5% of sunlight.” -Earther