Actually, a Japanese blog identified it as a quaint - and bizarre - little place called 菊や (Kiku-ya), which has since shut down.
The photos of the place, which you can find in Google Maps and the like, are quite an exact match.
I stand corrected - I seriously thought the crazy flavors on the ramen shop wall was part of a fictional gag but that the color changing noodles were real. Nope, someone did came up with all those crazy flavors, up to and including the ice cream ramen (which is a monaka ice cream bar sliced in half and served with noodles). Even the location (near the river bank with not much through traffic) is a bit absurd…the whole thing just felt like someone’s post-retirement hobby run out of their porch. But yeah, good find.
That being said, the chapter came out in Japanese on late 2014/early 2015, the Tankobon in late 2015, and the place closed down in 2017 (officially in August but openings were sproadic for a few months prior and mentioned on blogs covering Adachi ward businesses)…and if you do Google streetview (there’s one for September 2017) there is a handwritten notice at the front announcing closure. The Dark Horse Volume 2 TPB came out in 2020, so by the time the translated version of the chapter came out it has been gone for years.
My reading of handwritten Japanese and Kanji cursive is bad/almost non-existent but this is what I think it says on the door after the closure:
長い間
ありがとうございます
店主*痛決閉店
For the longest,
Thank you very much.
The shop owner made the painful decision to close up shop.
I just can’t figure out if the uncertain kanji on 店主[*]決閉店 on the note is 痛 (shi, or painful) or 病 (byo, or sick), most likely the former.
Even Kipposhi (that’s the place currently serving the color changing ramen) might not be around anymore since that boughie parts of Minato is dead-as-hell on the weekends and I didn’t see much recent entries about it on Tabelog.