Abstract: An assembly or set of different color inks (10), capable of changing their color by reduction, comprising at least one ink (12) including a reducing agent for the mentioned inks. When one of said reducible inks (10) is contacted with that ink (12) bearing the reducing agent, the reducible ink (10) is reduced, changing its color, and juxtaposition or combination (11b) of the reduced ink color with the reducing ink color generates a different color for each ink. These inks are useful for composing polychromatic figures, designs, etc. for didactic and artistic purposes and the like, with writing or drawing instruments, such as fiber pens.