We tend to think of light bulbs as simply creating "light", but depending on the type of bulb, it can have quite an impact on the colors you're seeing. If you're struggling with mixing paint colors, if something seems right when you do it then wrong the next morning, the problem may be that you're painting under artificial lighting.
In the photo above, all the walls have been painted with the same white paint. Yet the colors of the walls differ from the sink area at the back, which is lit by natural light through two large windows, and the studio area where the easel is standing, which has no natural light whatsoever.
Incandescent lightbulbs cast a warm, yellow light and fluorescent lightbulbs a cool blue, though you don't generally notice it except in photos taken without a flash. The ideal lightbulb for viewing art, or painting under, is a day-light one or a full-spectrum light, which gives a very clear bright light. I have a powerful full-spectrum desk lamp in my studio for dark winter days, though I do check the colors again the next day in natural lighting.
You don't have control over where a painting you sell will be hung nor the type of lighting it'll be seen in, so should you mix colors so they look right in artificial light or natural light? I think it's best to paint colors so they're right in natural light. You can't control what kind of lighting a painting might be hung in, but at least this way it'll look okay during the day. Art galleries should have