The index of blue, as a concept, offers a powerful framework for analyzing the intersections and tensions between different emotional states. In the context of "Normal People," blue is indeed the warmest colour, representing a complex interplay of warmth and coolness, intimacy and isolation. As we reflect on the novel's use of colour, we're reminded of the ways in which fiction can illuminate the human experience, offering a profound and lasting impact on readers.

Throughout the novel, Rooney uses blue to describe Marianne's surroundings, clothing, and even her emotional state. For example, when Marianne is feeling anxious or upset, her surroundings are often described as blue or grey-blue, reflecting her inner turmoil. Conversely, when she's feeling calm and content, the colour blue is absent or replaced by warmer tones.

In "Normal People," blue is more than just a colour – it's an emotional state, a mood, and a reflection of the characters' inner lives. The novel's protagonist, Marianne Sheridan, is often associated with the colour blue, which serves as a visual representation of her emotional landscape. Blue is calming, yet melancholic; it's a colour that evokes feelings of serenity, but also of sadness.