The colours have been cleverly arranged to enable the child, parent, or teacher to perform specific functions. As well as the obvious function of counting both forward and backwards. The multicolour abacus also can be used for junior science. For example it can be used to teach small children the colour wheel. By talking about the spectrum and how a rainbow works.
All children are interested in rainbows.
Our abacus will take this further. Assuming that indigo and violet are almost the same colour to the human eye. You can see from the illustration below the spectrum colours. As well you can discuss the 'Primary' and 'Secondary' colours. Also you can show how when colours are mixed together.