Red Rods:  In October 1922 Maria Montessori met with the Dutch manufacturers of the materials and some teachers discussing finer points of the colours and production of the materials. A report of this meeting was published in the magazine of the Dutch Montessori Society at a later date, containing some lovely and interesting aspects for today's Montessorians. During that meeting Maria Montessori explained why she wished the change in colour to the rods: she had found that children were attracted more to red than green (the original colour of the rods).

Pink Tower:  The earliest publication of Maria Montessori refers to Torre Rosa. We have found no evidence of it being any other colour.

Brown Stair:  There were earlier versions in blue but at one point the prisms changed to the colour brown. The original instruction by Maria Montessori was that the material was one solid colour.

Number Rods:  Old material on display in the Gonzagarredi museum shows the colours of the number rods used to be either red/yellow or yellow/green before the colours blue/red as we know them today.

From various historical documents, anytime a colour of a material was changed, it was based on Dr Montessori’s observations of children’s interests.