I bought a set of gels for my speedlight. Again, I’m baffled by the reduction in price for photo gear.
One thing you can do is to use the flash with gels and use that light color to set the white balance.
This picture is shot with tungsten white balance and an orange (tungsten) flash gel. The result is a very saturated dark blue sky. This is actually shot in broad daylight but it looks like it is late at night. The more flash power you use, the more pronounced the effect will be.
Slight adjustment of white balance post-production was needed. It still looks slightly off, but this is as good as it would get.