The drab dark days of December can get to you – except if you take charge. That is why we put up trees, and icicles – and that is also why you can use gels.
Like these Honl Photo gels, which I use on my speedlights all the time:
Red and green are the seasonal colours that can make a boring scene into an appropriately brightly coloured one.
Especially with the remote flash technique I metioned a couple of days ago:
So your assignment: today, go take a few pictures with a gelled flash – or preferably with two gelled flashes.