Yellow, Blue, Red — These three items share a single precise category in color theory. Identify that category from the options.

Introduction / Context:
Color theory analogies often test whether you can name the category that unifies a set of hues. Yellow, blue, and red—when presented together—are classically taught as the primary colours in traditional pigment mixing models used in art education (RYB model). The task is to select the exact category name that fits all three, not an associated but different grouping.

Given Data / Assumptions:

• Yellow, blue, and red form the canonical triad in the RYB primary model.
• We are using the common art/painting primary model (not RGB light primaries).
• Exactly one option names this category precisely.

Concept / Approach:
Match the list to the standard primary colour set in the intended context. In school-level art instruction, RYB primaries are used for subtractive mixing of pigments; combining them produces a range of secondary colours such as orange, green, and violet. Therefore, “Primary colours” is the correct unifying label.

Step-by-Step Solution:
1) Recognize the trio as the RYB primaries.2) Eliminate categories that contradict the given set (e.g., “secondary”).3) Select “Primary colours.”

Verification / Alternative check:
Secondary colours in the RYB model (orange, green, violet) are formed by mixing pairs of these primaries; hence yellow, blue, and red themselves cannot be secondary.

Why Other Options Are Wrong:

• Secondary colours: Formed from primaries; not the given hues.
• Warm colours: Blue is not warm; this category is misaligned.
• Paint types: A materials category, not a hue category.

Common Pitfalls:
Confusing light primaries (RGB) with pigment primaries (RYB). The stem’s trio corresponds to RYB primaries in art contexts.

Final Answer:
Primary colours