Solution

156662

First name
Amethyst Class
School
Colby School
Country
Age
11
Email address
office@colby.norfolk.sch.uk

To find the solution, the quickest way was to work in layers. If the centre cube of layer two is a certain colour, then that colour will not be shown as a diagonal on any faces. But the other colours will have three faces with diagonals each. The centre colour does have a diagonal in the middle layer and one 3d diagonal through the centre. We changed the middle colour and the outcome worked!
Colby School, Amethyst Class.