I’m a buyer and I don’t draw, but here’s my brief take on the process. I usually don’t get sketches of the work in progress. It doesn’t bother me personally though because I rely on revisions and my extensive initial instruction to carry the drawing from start to finish, accurately. Wow, people know HEX color codes? I had to google shades of colors and get photos and get some opinions until I could pick out a color. One handy tool is a mobile app called Color Grab that can detect any color on any part of an image. It could also just be a matter of “I’ll know it when I see it”. Yeah, personality and style are important. IMO, art, like anything else creative, is ultimately subjective and a form of expression. Knowing what emotion, personality or expression you want the drawing to convey is important. I actually think the expression is the biggest part. Art is simply visual expression, like how writing is verbal expression and music is…aural expression? It’s all expression, at the end of the day. A brand book is a good idea. Or just having some template so that all drawings maintain consistency across each drawing. It also helps people recognize what they are looking at, probably.