I've added the ability to hit a button to add a schedule to flip between green and red every 15 seconds to my page:
http://huetest.azurewebsites.net
You'll need to give it your hub IP and API key if you've not already done that. you'll have to work out your hue hub IP address on your network. My router page showed me mine.
Once you have the hub IP go to
http://huetest.azurewebsites.net/genapi.html and follow the instructions to generate the API data. This is saved as a local cookie, I am not storing anything, nor would I have much use for it even if I did as your hub IP is a local range.
This will work either on a whole group at once, or you can just hit the button for a single light of your choice. The green Bell icon will do it, sorry could not find a better icon to use in the material icons I am using.
You can delete all of the Festive light config globally by hitting the big "Delete Festive Lights" button at the very top of the page. The lights will remain on the last colour used though.
This does not require the page to be open to operate, the configuration is saved as a recurring schedule on the Hub itself.
At the moment I have not allowed the user to configure the frequency, or any transition speed effects, but it may not be impossible to do something with this. Just easier not to
There is a nuance around how the schedules work though, and this largely boils down to how I can issue a command to set something to change on a schedule, but I can't tell it when to start. As such the page has to wait for the desired interval before issuing the 2nd colour to switch to. This is largely using Javascript which doesn't have a wait/sleep function built natively into it. Kind of annoying but I've had to work around it. TLDR version of this sentence: If you hit the button to add festive lights you'll need to keep the page open for 15 seconds more at least so it has time to chill and add the alternative colour switching schedule.
I basically have to tell it to have a 30 second recurrence but to start 15 seconds apart from eachother.
Let me know how you get on?