Light is just wavelengths bouncing off your wall, and paint only reflects the wavelengths the bulb actually emits. Change the bulb, change the colour. It's that simple — and that brutal.
The two numbers that matter are colour temperature (measured in Kelvin) and CRI (Colour Rendering Index). A warm bulb at 2700K throws out yellow-heavy light, so it amplifies the warmth in a colour and quietly murders any blue or cool grey undertone. A neutral or cool bulb at 4000K+ does the opposite — it flattens the cosy yellows and pulls grey, green or lilac undertones forward, sometimes nastily.
Real examples mate. A soft warm grey like Farrow & Ball Cornforth White can go from gentle and pinkish under daylight to a slightly mauve or even cold cast under a cheap cool LED. Skimming Stone leans warm and creamy under 2700K but can read flat and grey under a high-Kelvin bulb. Greens are the worst offenders — Little Greene French Grey or a sage like Mizzle can swing green-to-grey-to-blue depending entirely on what's in the ceiling.
The killer detail is CRI. A bulb with CRI below 80 has gaps in its spectrum, so certain undertones simply have no wavelengths to reflect — colours look muddy and "off" for no obvious reason. Always buy bulbs at CRI 90+. This single change fixes more "the colour looks wrong" complaints than re-painting ever does.
What about "but it looked fine in the shop"? Showrooms use bright, fairly cool retail lighting. Your sitting room at 9pm under lamps is a totally different planet.
Practical advice: test your sample board under the actual bulbs you'll live with, at the time of day you'll use the room, not just by the window at noon. Decide your bulb temperature *before* you commit to the colour. Go warm (2700K) for living rooms and bedrooms, neutral (3000–3500K) for kitchens and bathrooms, and never below CRI 90. Sort the light first and the colour behaves.