Actually, it's always been there:

While writing your requests, do remember to specify the character you want written about, especially if it is a non-chromatic source with one or few chromatic characters. Your writer is under no obligation to write the character you might mention in your optional details unless you have asked for them in the 'characters' slot. If the chromatic character you want fic for is not listed in the options choose 'Any' and say how much you'd like fic focussed on that character in your request, and use a freeform tag like 'chromatic character'.

The paragraph hasn't been edited since as far as I know, speaking as one of the co-mods.