I wanted to do an activity about colours in an ESL classroom I was recently doing some relief teaching in. I looked for a colours poster or anything that had the colours on them. I couldn't find anything and so I taped some coloured pencils to the whiteboard.
Just after I had taped them to the board, I did realise that it would have been better to place the darker pencils down lower, as these were difficult for students to distinguish. It worked well though and was helpful to those students who had no knowledge of colours. They were able to take the pencil to the board and find the matching one.