This was, I think, before blueberries became poplular, and I have a vague memory of mashed potatoes with added food colouring being suggested.

I can’t think of any naturally blue food apart from blueberries and bilberries, and even they aren’t very blue on either the outside or the inside.

The part which I particularly noticed was about describing the colour of something as (the same as/like) the colour of (something named).

So, my wording, something like,

The colour of leaves in summer.

The colour of holly berries.

Another thing I noticed was saying that the colour blue was not widely known before industrialization.

There was ultramarine, as a pigment, from lapis lazuli, which was rare.

I have a recollection of something from years ago about making food in the colours of political parties.

Labour Party was easy, tomatoes. Liberal Party (as I think it then was) was easy, carrots, but there was a problem for Conservative Party. This was, I think, before blueberries became poplular, and I have a vague memory of mashed potatoes with added food colouring being suggested.

William