To most people color will be confined to the images that you produce. Most modern monitors are capable of carrying hundreds of images and also using extremely high resolution images can slow down download and load time of an Ebook. This is going to be a judgment call so just make sure your images aren’t blurry. When in doubt it’s better to sharpen an image with GIMP than what it is to increase it’s dpi.
These are the kinds of things we take for granted because whatever the size of a sheet of paper is and with Ebooks this is a little different. Make sure your page size isn’t wider than your average screen, and you might want to create your work on a desktop than a laptop. Laptop screens tend to be slightly wider than desktop screens, especially older desktop screens. If the reader has to skip back and forth than they are likely to miss lines making the Ebook incoherent.