This chapter explores the interrelationship between colour, art and the law. It considers problems for the law in regulating colour in art. It focuses on the potential to protect colours under Australian intellectual property law, but also explains how artists’ freedom to use certain colours may be legally curtailed under exclusive use contracts, trade secrets law, industry codes, and health law banning the use of harmful compounds. From a historical perspective, it argues that ‘soft’ law restricted the use of precious pigments available to artists. To illustrate the issues, it utilises two hypothetical case scenarios involving Yves Klein’s blue monochromes and recounts how ‘forbidden colours’ are at issue in contemporary controversies surrounding Klein’s patented colour International Klein Blue and Vantablack, the former being the most vivid blue ever produced and the latter, the blackest black. From the scientific literature on colour perception, the chapter distinguishes between colours as substances, appearances and perception. It discusses the difficulty in regulating colour when colour itself is subjective, and experiences not definitively predictable. In dealing with these challenges, the chapter draws implications for exercising creative freedom.