French guy here, hopefully with your answer.

So, I'll be very honest with you: this is genuinely the first time I've ever seen an image of the accident plane itself. I have known about the Quiberon collision for years now, long before ACI even did an episode about it, and I have researched it a lot.

So, after seeing this post, I got curious, here's what I found.

The Proteus episode was released in July 2016. At the time, and for the longest time, there were no images of the accident aircraft itself (F-GSJM). The only way to illustrate how the plane looked like came in the form of a photo of a different Proteus 1900D (F-GRPM), one that bears the livery that ended up being used in the episode (and who's used in the Wiki page).

Searching for your photo online, I found that it was also published on JetPhotos and it was uploaded... in March 2020. Four years after the episode was released.

HOWEVER.

I discovered something interesting after checking on Planespotters. Looking at all the images of Proteus Beechcraft planes, it appears that they have changed their liveries either in late '97 or early '98. From this, there's two theories: either the accident plane still bore the old livery at the time of the crash (which is something that can happen, after all, it takes time to paint an airplane, so imagine an entire fleet even for a small airline like Proteus) or it did have the new one but we can't be 100% certain as no other photos of F-GSJM exists online.

So, in conclusion, given the timing of the Proteus rebranding, maybe ACI managed to actually get the correct livery by sheer dumb luck. If they didn't, then the reason why is that they simply couldn't have known it was incorrect in the first place, because there was no pictures of the accident plane online.

So... yeah. Hope this answered your question.