An online colour-naming experiment was designed and developed to determine a broad set of colour words in wide cultural use with their corresponding colour ranges in sRGB and Munsell specifications. The quality of the English dataset was analysed in terms of colour centroids, frequency of names, consistency and response time. The importance of basic colour terms was confirmed while it was also revealed that in free colour naming tasks, the majority of the observers preferred to use non-basic colour terms. The validation of the web-based experimental methodology with previous studies conducted in controlled viewing conditions produced satisfactory results, while a comparison of the 27 most frequent chromatic colour words with a previous web-based experiment showed a remarkable agreement.