The color of the seaweed was shockingbright green, so it didn't look appetizing.

"Shocking green" (ショッキンググリーン) isn't used in English. To describe a very bright, eye-catching green color, native English speakers would typically just say "bright green." Sometimes neon green, electric green, and vivid green are used too if you want to be very specific.

I searched for the shop online, but I couldn't find thea picture of the onigiri.

I found someone's blog where they explaining the food in the shop, "Wasabi," in London.

However, the "Nori oOnigiri" looked different from the one in New York.

Why I didn't take thea picture😭 ¶
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I just want to show everyone the color...

The color of the seaweed was shockingly green, so it didn't look appetizing.

I found someone's blog where they were explaining the food in the shop, Wasabi in London.

Why I didn't I take thea picture😭 ¶
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I just want to show everyone the color...

I bought an interesting onigiri when I was in New York City.

I think most Americans call it nigiri, and drop the 「お」. As far as how we pronounce it, oof, it's not at all correct! We say it a little bit like ニッギーリー, except the sound we use for 「ニ」 doesn't exist in Japanese, nor does the sound we use for 「リ」.

The color of the seaweed was a shocking green, so it didn't look appetizing.

"shocking" is a weird word to use to describe a color. Some more natural sounding words could be:
"a weird green"
"an unusual green"
"the wrong green"
"a sickly green"

I assumed it contained some artificial color.

"assumed" implies that you USED TO "assume it contained some artificial color," but now you don't. Where as "assume," means that you STILL "assume it contained some artificial color."

I found someone's blog where they explaininged the food in the shop, Wasabi in London.

Since the person already wrote the blog (in the past), then that person had already "explained the food in the shop", so it uses "explained". If you wanted to instead use "explaining," then you would say "I found someone's blog explaining the food in the shop." This is because "the blog" is doing the explaining (and is still doing so), so it would use "explaining."

I'm confused by what you mean with "Wasabi in London." is that the name of the blog (then the sentence should be "I found someone's blog, Wasabi in London, where they explained the food in the shop.")? Or is that the name of the shop (then the sentence should be either "I found someone's blog where they explained the food in the shop (Wasabi in London)." or "I found someone's blog where they explained the food in the shop, which was called Wasabi in London."). English is weird, in that in this special case, it's unclear whether you are applying "Wasabi in London" to the "blog" or the "shop," but through my initial read, it sounded like "Wasabi in London" is the name of the blog.

Why I didn't I take the picture😭 ¶
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I just want to show everyone the color...

I bought an interesting onigiri when I was in New York City.NOTE: If readers understand Japanese, then "onigiri" might work well. Some readers who do know Japanese might the prefer the term "rice ball."

ALSO POSSIBLE: It was called "Nnori Oonigiri," a rice ball with sea laver."

ALSO POSSIBLE: I showed my friend the onigiri, and she was also surprised by theits color.

MY PREFERENCE: I searched for the shop online, but I couldn't find the picture of theat onigiri.

I found someone's blog where they explaining the food in the shop, Wasabi in LondonMY GUESS: I found the Wasabi blog in London, where they explained that shop's food.

CLEAR: However, the Noriat onigiri looked different from the one in New York.

Why I didn't take the picture😭 ¶
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I justALSO POSSIBLE: I should have taken a photo of it, wanting to show everyone the color..its weird color to everyone.