One easy method is to consider the light and mood you want in the room. Warm colours (creamy whites, beiges, soft peaches, warm greys) make spaces feel cosy and inviting. They work well in living rooms, bedrooms and areas where you relax. Cool colours (cool whites, blues, greys with a blue or green tint) feel fresher and more crisp, which suits bathrooms, some kitchens or very bright rooms that risk feeling too hot.
Look at the natural light in the room at midday. If it already leans cool and bluish, a very cool colour might make it feel chilly. In that case, a warm neutral balances things. In very sunny, hot rooms, a gentle cool tone can be refreshing.
A quick trick is to paint a small sample on the wall or use large sample cards and observe them at different times of day. Your eyes will tell you pretty fast which side – warm or cool – feels more comfortable to live with.