- a dark-blue pigment consisting of a mixture of cobalt and aluminum oxides
- dark blue
cobalt bluecobalt blue
- A blue to green pigment consisting of a variable mixture of cobalt oxide and alumina.
- A moderate to deep vivid blue or greenish blue.
- The color of the pigment zaffre.
- In September these are nearly covered with flowers, arranged in close trusses at the ends of the shoots, and of a fine cobalt-blue, changing to violet; they usually last till the frosts.