Since she said she knows how he can see colours again I have a theory, tho it's loose and just based on my own ideas:
He can see colours based on emotions he can feel. Red being anger/rage/etc.. So she can teach him emotions and hence teach him to see colours.
Is my idea as a hobby writer anyway. Might be something entirely different in the comic. X'D
She mentioned she was the author of the story, so she likely knows how to fix him and will explain it soon/later on.
Ohhh!! That was kinda explainable XD I thought they just kinda made it that way, because they I thought they can't think of anything of a dialogue XD
Well...that could also turn out to be the case. I've seen that stuff happen before and was VERY confused since the idea I had seemed to fit the plot hints but then BAM, the regular 'it is so because the author says so' reason.
But I do really hope I'm right with my guess. XD
Meh XD We can't do anything about that phrase XD
Wait a minute, they said that he can only see black and white right? Then, how did he know what color our fl's hair color is if he hasn't even any other colors other than black and white?