A good point, could there be a color background which the thermal printer prints on top of? Even if that's not possible from the full examples it looks like most of the color is branding related so could be converted to black and white.
Yes, this is pretty common for printers installed in service desks at the airport. However, they tend to not have overly-branded stock because in the irregular circumstances you tend to get a pass from a service desk, you might be rebooked on a different carrier, and would therefore have a mismatched boarding pass.