There's two types of color e-ink displays on the market.
ACEP displays use different sized CMYK pigments in the display, which can be selectively exposed or hidden. They provide a similar resolution as well as brightness and contrast to monochrome e-ink displays, with high color saturation, but a slower refresh rate, and poor color accuracy, especially on primary colors of light (RGB).
CFA displays use a standard monochrome e-ink, overlaid with an RGBW color filter. They have the same speed as the underlying monochrome e-ink displays and high color accuracy, but the saturation is low, and the image is blurier, darker, and lower contrast than monochrome or ACEP panels.
ACEP displays are also more difficult to get, as far as I know only available in the now-discontinued BigMe Galy (https://www.kickstarter.com/projects/bigme/galy) and the in-production Remarkable Paper Pro (https://remarkable.com/products/remarkable-paper/pro) and Pro Move (https://remarkable.com/products/remarkable-paper/pro-move) devices.
If you must have vibrant colors, at any price, don't need particularly responsive scrolling animations, and want to be able to use the e-reader indoors with the frontlight off, get an ACEP display.
If you want the most accurate colors, don't mind low saturation and contrast, and will be using the e-reader outdoors or with the frontlight on when indoors, get a CFA display.
If you want an e-ink display that is really fast or one that is easy to obtain and visible indoors without a frontlight, your only option as a monochrome display.
I've used all three technologies, and I selected a monochrome display for my daily driver, a HiBreak Dual cellphone. If there were an ACEP version available, I would have bought it, but it's almost never an option, and the darker and blurrier CFA display wasn't worth the small amount of color it provided.