[okonomiyaki3000]

They are green. Japanese people just call them blue (青). The colors we call green and blue are just ranges on a spectrum. Where you draw the line between them to call one green and the other blue is partially a matter of personal perception and maybe more a matter of culture but there is no absolute right answer.

I'm not sure if there's any connection to why Japanese tend to lean towards blue rather than green but the Japanese word for green, midori (緑) is linguistically different from most other colors. It doesn't have a true adjective form and is instead used as a noun or "adjectival noun". Does this difference create a subconscious aversion to it in the Japanese psyche? I really have no idea.

[rhplus]

We also call traffic lights “green” in North America and Europe, but if you look carefully they’re actually in the “cyan” color family, much closer to turquoise or aquamarine than a green.

https://en.wikipedia.org/wiki/Web_colors