Because our data comes from our books (ie not a database), the colour coding is done automatically via text matching. This means that no two grades can have the same text representation, which becomes a problem as we add more grade systems (Scottish and UIAA in particular overlap a lot).
This guide has the grade "D" in it. At some point we had to change that to "Diff", because "D" is also used for "Difficile", which is orange I think.
I'll have to go through that book and change all the grades to Diff to fix that error.