Interesting. Could you share some of that research and its conclusions?
Of course, there are several possible error sources (unfamiliarity with the colouring scheme for example), and whether this can be transferred to reading code is an open question. But I still think it's important to keep the existence of this kind of research in mind when discussing this kind of question (and also the similar question of mouse-driven interfaces vs. keyboard shortcuts), as it easily devolves into strongly held opinions and arguments along the lines of "it stands to reason that $opinion-held-is-true"
In code, I'm frequently tracing back and forth through a block, looking for specific information in different lines. I think that the coloration helps to provide "landmarks" for non-linear traversal of the code. I'd consider color-free code to be more similar to un-punctuated text, than I would consider colored text to be to colored code.