Here is my latest stained glass effort, seen on a snowy day.

It is a 'square of squares', where all the constituent squares are of different sizes. Here are the dimensions -

It is copied from the logo of the Trinity Mathematical Society, who point out that it is the unique smallest simple squared square (smallest in that it uses the fewest squares, and simple in that no proper subset of the squares of size at least 2 forms a rectangle). It was proved to be the smallest such square by Duijvestijn in 1978, but this was by exhaustive computer search, which seems a bit like cheating.

There is a fine Wikipedia site which contains more than you ever wish to know about squaring-the-square.

Challenge

I wanted to only use 4 colours without any square touching another of the same colour, and of course I knew this is possible due to the 4-colour theorem. But I wanted the four large outer squares to be 'white' (in order to increase the Mondrian appeal). It took some effort and trial-and-error to find a 4-colouring with this property. Are there others?