So what's with the "rainbow" color scheme in this artist's conception of sail-propelled spacecraft, drawing propulsive energy from the light of the Sun?

This is the Diffractive Lightsails concept. It's something new from NASA. These sails would not work by reflecting sunlight, which is a concept that has already been tested.

quote Shortcomings of the conventional reflective design include sails that are big and thin. They’re also limited by the direction of sunlight, which serves to constrain either power or navigation, as you can’t have both. Diffractive lightsails, by comparison, employ tiny grates on the sail material to diffract light in all directions. As NASA says, this will allow spacecraft to “make more efficient use of sunlight without sacrificing maneuverability.” The design ... could result in smaller and nimbler sails. And as a fun side effect, the sails would be rainbow-patterned, similar to how CDs look when held to light.

"NASA moves ahead with 'wild' solar sail concept"
George Dvorsky for GIZMODO; May 25, 2022.
https://gizmodo.com/nasa-so...ightsails-1848971175

The use of tiny diffracting grates, instead of shiny, reflective surfaces... tiny beats shiny..!

Who knew?

[This message has been edited by rinselberg (edited 05-27-2022).]