Melanizing is adding pigment. I've always heard it used in referrence to black pigment, but I suppose it could also be used for red. Henk?
In terms of e^b and E^R, melanizing can add black pigment to the non-black areas--turning e^b brown to black, turning E^R hackles and saddle that would normally be cream (in the case of your BCLB) black instead.
So, if the feathers that would be cream are melanized into black, which is diluted to blue, ig will have no affect, even though present.
Kind of like adding bleach to the wash of brand new clean whites--you don't see the affect of the bleach, even though it was there. But if instead of new whites, the washload is full of darks, you'll see the fading it caused.