When a signal has a very big growth in a month, MQL5 system doesn't count it against the overall growth of the year and put it in this grey color.
Here is the signal that was posted for my example - just in case if anyone here is able to calculate that manually or know the answer to why it is greyed, I don't know.
The first few months on 2016 were greyed. Apr to June were lower than 10%
Maybe, just maybe, as I do not know for certain, both you and Alain a correct and a more simplified general answer is: Grey Values = Unverified/Unverifiable Values!
So, values before registration are obviously unverified, and values that somehow fall outside normal statistical allowances are also unverifiable!