The Ishahara conundrum 2

Three days ago I blipped a house number, made in mosaic, that I see on one of my regular walks. It looked for all the world like a colour blindess test. Now I have started seeing them all over the place! This one looks like a deeply personal work of art and I have to say I like it. I wonder when it was made. Was the source a favourite plate that bit the dust?
Anyone else see these regularly?