I was watching the (eventually scrubbed) launch of Delta IV Heavy with the Parker Solar Probe. I noticed a fairly large blue/red flare near the launch pad. I'm guessing it's LH/LOX, but I thought hydrogen burns more yellowish.
This Reddit question may address the same topic, but I couldn't find the flare in their screenshot.
Below is a screenshot (literally a photo of TV screen... sorry) with the flare in the bottom left.