Amazon can also process content in EPUB source format. KindleGen compiles the file and runs checks for common errors. Any errors or warnings will prevent the titles from becoming available. These errors must be fixed in the EPUB file before the title is published in the Kindle store.
Body text should not have an imposed font color throughout the book. If you prefer to use imposed font color in some sections of your book, please do not use too light or too dark color. Light colors will not display with enough contrast on devices set to white backgrounds or on e Ink devices. Dark colors will not display well on devices set to black backgrounds. For grays, use colors within the hex value range of #666 to #999.
Body text must not have a white or black font color. Customers report this as a bad user experience because the text can become invisible when the Kindle is set to the same background color as the font.
Body text must not have a black or white background color. Customers report this as a bad user experience because it can create an awkward, boxy reading experience when the device background is set to a different color and because the text can become invisible when a user changes the background color setting on their device and the font color automatically inverts.