I reread the comic a while ago and at this page I remembered while reading chapter 4 for the first time I was a bit confused when the problem came up that the spectral energy colour of Dr Zarei didn't completely match up with that of the Ghost Train. With the new archive lay-out I noticed the Ghost Train's energy changed from being a yellowish green on page 106 (almost exactly like that of Zarei) to a more tealish green on page 123.
At first I thought it might've been a consequence of grudging out but on the last page with the yellowish green energy the Ghost Train was already a grudge.
That their energy colours were far more similar at the start of the chapter than at the end is especially visible in the last panel of page 71.

Now I'm wondering if the energy actually changed hue or if it was just a last minute switch made for storyline purposes to have their energy colours not completely match...

Does anyone have any thoughts on this?

I think it may have been unintentional -- Between page 71 and page 112, when they first board the train and when Zarei attempts to control the train's tool, the art style has changed significantly. In my opinion, the difference in the train's hue of spectral energy may have just been because of art evolution, or more specifically, a change in how the comic is colored.

I guess that could be the reason... Colour consistency seems pretty important in a comic with specific colours tied to specific characters though.
And the artstyle didn't change that much in the time the switch actually took place. Which in real life time was about a month between page 106 and page 123.
I guess it's kinda impossible to know without actual feedback from Zack himself, though I don't have the nerve and/or correct social media accounts to actually ask him directly >_>
I kinda stick to forums because I refuse to make a Twitter/Tumblr/Reddit account eventhough this place is pretty much abandoned...

Haha, I don't really use social media either lol