The presence of which of the following oxides imparts deep blue colour to glass?

Cobalt oxide (specifically cobalt(II) oxide, CoO) has been used for centuries as a coloring agent to produce deep blue glass and ceramics known as 'cobalt blue.' The cobalt ions in the glass matrix absorb light in the red and yellow regions of the spectrum, transmitting blue light. Iron oxide gives colors from yellow to red, while nickel produces green to brown tints.