A proper representation of the semantics of colour descriptions is necessary when colour information needs to be processed semantically, such as in the area of information integration. Semantics-based methods can help information from different sources to be integrated more easily and make final results more accurate and understandable among different sources. This paper introduces an ontology-based representation of the semantics of colour descriptions. By using a quantitative colour model and a Description Logic (DL) with datatype support, the semantics of a single colour term can be represented. Multiple such terms are then combined to generate the semantics of a complex colour description, which is interpreted by using morpho-syntactic rules derived from the analysis of colour descriptions in botanical documents. A colour reasoner, interacting with the FaCT-DG DL reasoner, can support colour-related queries and give domain-oriented results.