Are you intimately familiar with the inner workings of your heatpump? Nearly all heatpumps in a cold climate have backup heat built in and it would automatically switch to backup when it gets too cold outside. -30C is well into the too cold category for it to function as a heatpump alone
During the day it’s white, but it’s also overhead and blindingly bright so we don’t spend much time looking at it. As it gets closer to the horizon Rayleigh scattering begins filtering out the bluer light and the sun becomes yellow, then orange, then red. It also gets closer to our eyeline and becomes mildly safer to look at so we look at it a lot more. This in turn leads us to believe it’s always yellow