The use of the coloured stripe in the dialogue boxes to distinguish between Julian and Ash as first-person narrators is not only useful and clever, but the UI person/team did a great job of unobtrusively yet distinctly incorporating it as part of the VN's overall visual style. There are many other larger aspects of this VN that are also well-executed, as other comments have no doubt made clear, but that particular detail was the first thing that I noticed and was impressed by as I read this story. The level of attention to detail on many levels is exemplary, and the idea of the chapter recap feature is ingenious as well. This is a fabulous team working on a wonderful project, and I would gladly support monetarily if I had the means; as it stands, however, I eagerly await the next public update.
I had noticed that as well, but did not connect the dots until you mentioned it. If they were more defined abstract patterns, like futuristic arabesques or geometric linework that each fit the 'feel' of their respective narrators, I think that might make the difference a bit more distinguishable while still retaining the subtlety. In any case, I am sure that your final design choice will look great, whatever it ends up as.