Whether or not emoji are displayed in color on Windows systems has to do with which OS, browser, and fonts you have installed. For instance, on the Windows 7 PC I am currently using, emoji appear in black-and-white in Chrome. In Firefox, they appear in color — but it’s only a simplified color display, often monochromatic, as opposed to the detailed, multi-color emoji characters one sees under Windows 10. (I see I’m running three emoji fonts at the moment — EmojiOne Color Regular, Noto Emoji Regular, and Segoe UI Emoji Regular — so I’m not sure which is being used by either browser. Seemingly, Chrome uses a different font than Firefox, as Chrome only displays emojis through the Unicode 6.0 definition, while Firefox displays Unicode 7.0 characters.)
Google 'color emoji [OS] [browser]' for instructions on how to configure your particular set-up for color emojis.
