O-Chul's story will be done in the current art style, as will everything from now on unless I'm trying to specifically insert material into the middle of an older story for some reason, such as when I drew the bonus materials for Blood Runs in the Family. There wasn't any art completed on the O-Chul prequel beyond that cover image until recently, only outlines and scripts, so there's no need to match the older style if I don't want to (and I don't want to).

O-Chul's story will also be greyscale. The bluescale is nice in theory but the big problem with it is that without color, my art relies heavily on that black line to differentiate between blocks of grey that are sometimes only a little bit apart. Every blue I tried failed to do as good a job at separating darker tints (60-80%) as black does when separating equivalent greys. And any blue that even came close looked more like grey or purple when scaled back to 10-20%. The only way to make it work would have been to use different blues for different parts, at which point you're using multiple inks when printing and you might as well work in full color. The main reason I started using greyscale in the first place was due to the massive cost savings of 1-color printing anyway.