Question about LG OLED55C29LD

You are right, the colour is not the only difference. The more expensive model (C29) has a swivel base, but this does not differ visually from the C27 series. In addition, only the model of the C29 series is compatible with the so-called "WiSA 2.1" transmission standard, with which audio signals can be transmitted wirelessly with up to 24 Bit/96kHz including Dolby Atmos. You only have advantages if you also have a sound system or, for example, a soundbar that also supports this standard.