The colors and the weird s were both from the 180 year old version. The interactivity is new. Here's the author's thoughts:
> Creating a faithful online reproduction of a book considered one of the most beautiful and unusual publications ever published is a daunting task. Byrne’s Euclid is my tribute to Oliver Byrne’s most celebrated publication from 1847 that illustrated the geometric principles established in Euclid’s original Elements from 300 BC.
> The long s (ſ) was common in older publications and is used throughout the book. Even though it’s commonly mistaken for the lowercase f, I felt reproducing it was also important to stay true to the original.
> I wanted to add interactivity to the diagrams to aid in understanding them because I had some trouble understanding some in the original book.
Here's lots more thoughts:
https://www.c82.net/blog/?id=79