Canonical Color as a Lens into Concept Decodability in Vision Encoders and VLMs

Xiaofu Chen, Stella Frank, Yova Kementchedjhieva


Abstract
Vision encoders construct the image representations used by vision-language models. How much conceptual information, rather than immediately visible image evidence, do these representations contain? We use canonical color as a controlled test case: can a vision encoder represent the typical color of an object concept, such as yellow for bananas, when visible color is removed from the input image? We construct a dataset of objects with canonical color labels and probe vision encoders for both color and object identity using RGB and grayscale inputs. We find that canonical color remains decodable from grayscale images and is tied to predicted object identity, suggesting a conceptual link between object and color information. Extending this analysis to full VLMs, we find that VLM post-training can have a surprisingly large effect on color decodability in the vision encoder. Overall, canonical color provides a controllable lens for tracing object-level semantic information in vision encoders and VLMs.
Anthology ID:
2026.emnlp-main.1291
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
29413–29424
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1291/
DOI:
Bibkey:
Cite (ACL):
Xiaofu Chen, Stella Frank, and Yova Kementchedjhieva. 2026. Canonical Color as a Lens into Concept Decodability in Vision Encoders and VLMs. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 29413–29424, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Canonical Color as a Lens into Concept Decodability in Vision Encoders and VLMs (Chen et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1291.pdf