Typically I drag tools from the tool pallet to my workflow. Sometimes, when I need to insert a tool into my workflow, I will right click to get the Insert tool dialog to find the tool I want to insert between two existing tools. With the new UI, it is hard to see the tool categories as these were redesigned for the darker back ground. The preparation category is sandwiched between 3 other categories that start with "P" and I typically lean on the color/shape of the tool icon to find what I'm looking for. Now I have to read the text to really know for sure.
Perhaps you could lightly shade the middle of the tool category icons to make them easier to see or perhaps make the background behind the tool categories match the new toolbar color.
Tool categories icons are hard to distinguish since they are now just light colored outlines on a light background.