einstein’s legacy (http://www.einsteinslegacy.com) has created Achroma 1.0.1, an image manipulation tool developed exclusively for macOS.
The app lets you removes colors from your images by providing two conversion modes; you can select from a set of preset color ranges or create your own collection of user-defined color ranges for processing. Achroma also lets you export images in a variety of formats, create interactive slideshow presentations and share images using various internet services.
Achroma requires macOS 10.11 or higher. It’s available for $9.99 from the Mac App Store in the Photography category.