Hmm, am I the only one using Skitch on Mojave in Dark Mode?
The latest Skitch update (2.8.4) appears to attempt to support Dark Mode. However in the UI many of the elements (including text) haven't been updated to be seen on a dark background. Therefore we have dark text on a dark background, which makes things difficult to read. Note the elements along the bottom of the Skitch capture window in the attached screenshot.