Solution

This puzzle deals with color channels. It is similar to Simon Sends in that it uses additive color mixing, but it has a fourth “brightness” channel in addition to the typical red, green and blue. This 4-channel color system was used in text mode on computers running DOS in the 1990s.

Separating the color channels yields a set of letters and symbols to be read vertically:

Channel	Image
Red
Green
Blue
Brightness

The symbols can be decoded as Emoji Math, yielding the clue phrase UNICODE 9660. The name of the referenced Unicode character is the solution.

BLACK DOWN-POINTING TRIANGLE