Colours shift depending on the light source. Daylight might make a colour look crisp and cool, while warm evening bulbs can make it look beige or even slightly yellow. The opposite can also happen – something cosy in artificial light might look dull in plain daylight.
Since you use the room in both conditions, you need to like the colour in both. Checking samples during the day and again after dark, with your actual lights on, gives the full picture.
You may decide to adjust your bulb colour temperature (warmer or cooler) based on how the paint responds, or choose a slightly different shade that behaves better overall.
Skipping this step is one of the main reasons people are surprised by how a colour feels once the painters are gone.
