Notice: This was edited by me to add a proper hour field. Original author: https://github.com/dneuman/clock
This is a simple browser clock that is based on (read: basically a copy of) dneuman's code. It uses the internal clock time, and so has all the time features of the device. It does not have any other features such as colour change, alarm, or 24h clock. You can easily clone this project and make the changes you want, though.
To use, just point your browser to https://tylerwdoesstuff.github.io/clock/index.html.