After a week's careful consideration, I finally said yes to SO the Prussian Blue PM Gaby!
Please allow me to share my experience to thank for all your kind advice.
I started missing the Prussian blue a few days after the discussion here but I'm still unsure if I see it as the mere substitute of Peacock. As many of you have suggested, this particular colour is exceptionally difficult to be captured by any photos. So I went on with some research and found
this YouTube video featuring the Prussian Blue Madeleine Strap (it's a very tempting bag too):
Videos capture a truer colour as your see how it changes under different lighting/angle and would be a useful reference if you are particular with colours

The blue is livid, leaning more on the ocean side than green. It looks "quieter" under indoors lighting and plays a more lively key in sunlight.
The video reassured my worry of having an overly loud fresh blue but I didn't decide until seeing the swatch again in person, this time under the natural light outside the shop (smart tip from
@m_ichele). And it's a YES! Another surprise in SO-ing a Moynat bag is the tailor-adjusted strap. I'm petite (158cm) and often find straps too long for me. I like carrying it over my shoulder and have the bag slightly above my hip level. Instead of punching 3 extra holes, My SA suggested shortening the total length so the tail wouldn't stick out as much.
The SO charges the same as a ready-made bag (around $4570 USD) in my home country so it's hard to say no. GHW and PHW charges the same and there's no extra cost in tailoring the length of the strap. It's expecting in 6-8months and weeeheee it's always exciting to have something to look forward to! The purchase just made my perfect day I was literally hopping out of the boutique in joy

!! Again, it's important that the bag is really something you want rather than a 2nd tier substitute (it's expensive dear!!). Thank you all for the collective wisdoms and I'll post photos on its arrival.
@konacoffee Congratulations! It's probably the last piece of SO in peacock worldwide (according to my SA)! Lucky you! Looking forward to photos on its arrival.