There is no evidence the rooster is a mix and not a split.Thank for all that useful info. So back to the original question, the rooster is a mix, not a split, it will throw mystery colors.
Blue Mottled to Millefleur = ½ Black Mottled, ½ Blue Mottled
Pair F1 Blue Mottled to Millefleur = ¼ Black Mottled, ¼ Blue Mottled, ¼ Millefleur, ¼ Blue Millefleur
* May have problems with Mottled progeny having gold in neck hackles, etc, or too much black in neck hackles of Millefleur. The Mottled with gold in neck hackles are good for pairing back to Millefleur & Buff Columbian but not necessarily of Mottled show quality.
There are also a few pics on different threads of Blue mottled split to MF that look exactly like the OPs Roo.
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