Wiktionary
alt. (context computer graphics English) graphics with two bytes of storage per pixel, allowing for up to 65536 different colors n. (context computer graphics English) graphics with two bytes of storage per pixel, allowing for up to 65536 different colors
Wikipedia
High color graphics (variously spelled Highcolor, Hicolor, Hi-color, Hicolour, and Highcolour, and known as Thousands of colors on a Macintosh) is a method of storing image information in a computer's memory such that each pixel is represented by two bytes. Usually the color is represented by all 16 bits, but some devices also support 15-bit high color.
More recently, high color has been used by Microsoft to distinguish display systems that can make use of more than 8-bits per color channel (10:10:10:2 or 16:16:16:16 rendering formats) from traditional 8-bit per color channel formats. This is a distinct usage from the 15-bit (5:5:5) or 16-bit (5:6:5) formats traditionally associated with the phrase high color.
Usage examples of "high color".
She was pretty, with dark hair and high color, but she was no fun on a party.
Bertrice stood over me, high color in her face now from her anger, but she'd gone quite still.
His expression was still wary but had lost some of that high color and unnerving intensity.