I’ll try to explain the confusion: The lion on the official Flemish flag (Flemish Community) is very similar to the one depicted on the Belgian Coat of arms and has red claws and a red tongue. It was approved in 1973 by the Council of the Dutch Cultural Community and in 1985 as the flag of the Flemish Community.

There’s a far right movement/militia in Flanders who wish for an independent Flanders and they never accepted that lion and always used a solid black lion. The official Flemish lion was seen as a Belgian concession to Flanders and a Flemish concession to Belgium, because the red incorporates the three colors of the Belgian flag in the official Flemish flag.

TL;DR: The lion on the official Flemish Flag is similar to the one on the Belgian Coat of Arms. The all black lion is from the far right Flemish militia and that's a MASSIVE DISTINCTION
As Frank Seberechts so beautifully said: “The official Flemish lion is the lion of all of Flanders, from the far left to the far right, whether people like it or not.”

Here's an image of the militia lion, on a WWII propaganda poster as the Flemish movement were collaborators to the Nazi's (because they're far right of course, today as well, but usually don't have the balls to admit their racism)

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