Blue hour vs golden hour
Blue hour sits in civil twilight: after official sunset (or before sunrise) while the sun is still no more than about 6° below the horizon. The sky holds a deep blue, street lights start to balance with the remaining daylight, and it is a favourite window for cityscapes and portraits with a clean backdrop.
On Sunwindow, evening gold ends at official sunset and evening blue runs from sunset to −6°. Morning is the mirror of that. The two windows meet at the horizon; they do not overlap in this definition. At high latitudes in midsummer the windows stretch, and above the Arctic or Antarctic circles the sun may not set at all — the ticket will say so.