If you happen to see the book of selections from R. H. Blyth titled Essentially Oriental, you will find this verse, written by Blyth in Japanese, given in the introduction:
葉がくれに 青い夢見る かたつむり
Hagakure ni aoi yume miru katatsumuri
And the translation given there is:
Behind a leaf
Dreaming a blue dream
I would translate it differently:
In the leaf shadows,
Dreaming a green dream —
While in modern Japanese aoi can mean blue, in its older use it meant green; it uses a borrowed Chinese character (青/qīng), which could mean blue-green, but in relation to leaves, it would commonly be understood as signifying the color green.
So this is how I understand Blyth’s verse:
A snail is in the leafy shadows, seeing only shades of green, and at that moment, this is its unthinking life — a green dream.
I strongly suspect that Blyth’s inspiration for this verse was the English poem “The Garden” by Andrew Marvell — specifically the last two lines of this stanza:
Looked at in the cold light of science, can a snail even see colors? Well, many say no, but there is some evidence that they can make distinctions, though whether this would be seeing color as we do is yet another question. Of course if Blyth were to read this, he would probably give a sniff of derision, because his attitude is that of Zhuangzi/Chuang Tzu, who, on seeing fish swimming about in the river, commented to his companion that they were happy. His companion then told him, “You are not a fish. How do you know they are happy?” Zhuangzi replied, “You are not I. How do you know that I don’t know the fish are happy?”
So basically, in this verse Blyth was writing like Issa, putting himself into the snail. And that is what we see here: Blyth as snail, dreaming a green dream in the green shade of the leaves.