"piros" and "vörös". if you just want to describe a color you see, then "piros" is brighter, "vörös" is darker. there are some cases where you can't use them interchangeably, but you are less likely to make a mistake if you stick to "piros"
As I understand, 'vörös' is mostly used to describe something more emotionally charged, since it's etymology goes from 'vér' – blood. It's likely to be used in figurative speech, whereas 'piros' only describes the colour.
That's actually a good one. My guess would be that we haven't supposed to learn that yet.
I cannot figure out why some lamp is already red, unless, as you say, it is a traffic light. Any native speakers to explain whether the sentence is about a traffic light? Or something else?
Because it's this one lamp in particular that we discuss. Honestly, this mixture of slavic and germanic grammar drives me crazy:)