Originally Posted by DMSmillie
Hi Jim - if you're planning to convert the images to greyscale for the MOBI version, because the Kindle only displays greyscale, I'd recommend not doing so. The "Kindle for..." applications (Kindle for PC, Kindle for iPad, etc) all display colour images, and it would be a shame to lose that facility. Also you never know - there might be a colour display Kindle just round the corner.
I agree, but...
Many, many color images don't convert to greyscale well using quick "default" methods (generally simply desaturating). The screenshots posted show several failures (note the man's pants against the table in the 3rd image and the text on the car in the 4th). To create the best images you need to adjust the colors in the color image so that the simple greyscale conversions yield good images (using lighter blues for the man's pants in the former and a lighter red or perhaps a different color like yellow on the car).
Use color images in the book but be sure to test the display on a monochrome/B&W display (e.g. Kindle Previewer for PC or Mac). Edit the color images in such ways as to create images that display well in B&W. If using an image editor like Photoshop, you can preview the B&W results by reducing saturation to zero. Don't use any of the app's more advanced conversions to greyscale for preview purposes. Those can yield better results than will be seen on the ereader.