Methods and apparatus for representing images using a compact color feature vector. A color feature vector includes a color element for each color in an image-specific set of colors. A color element includes a color identifier and a relative color occurrence. A compact color feature vector may be used in a content-based image retrieval (CBIR) system. The CBIR system includes an image data store containing multiple images. A color feature vector data store includes a variable-length color feature vector for each image in the image data store. A computer program receives a query and uses the variable-length color feature vectors in the color feature vector data store to identify which images satisfy the query.