Apparently I'm imagining things. I swear I saw it just a week or two ago show a 50/50 split out of enchi cinnamon to normal, but I just checked it again now and it's showing them as if they are not allelic. Either way, I stand by the rest of what I said and just wanted to correct that bit.
JKR and MCC have both had multiple clutches that seem to confirm it allelic though. One clutch, two clutches... odds can be a bit crazy sometimes, but when multiple people are seeing it repeated without any evidence to the contrary I think it's too strong of evidence to deny.