Mostly Zieler brand art markers. The colors blend well into themselves, although they tend to bleed out at the edges, so it can be tricky sometimes to color tight spaces. I have a few other random brands, like what I did the skin with, but those do tend to get those ugly lines, and I try to only use them for relatively small areas. My previous 3 drawings were all done with them rather than my Zielers and I can tell.

Also you absolutely need a piece of cardboard spacer or the markers will bleed onto the next page.