Your uniform defines you, wear it with pride. When you step outside the temple walls, these clothes you consider ordinary will be a symbol of your commitment to your lifelong calling (Jedi Master Morrit Ch’gally)
The Jedi did have somewhat of standard uniform in their order: robes, tunic, boots, and a belt. They were a symbol of humility, as they rarely wore any other clothes, and were just as sacred a possession as their lightsabers.
However the Jedi were afforded some choice during their time as padawans and knights over things like colour and style, but often these choices were made based on their species, mission, fighting style, etc.
Therefore it wasn’t really the Jedi council’s place to tell Anakin he couldn’t wear black robes. He wasn’t the first Jedi to do so, nor was he the last, and there is nothing inherently evil about a colour.
And as a movie making decision, Anakin was made to wear black robes to resemble Luke when he became a Jedi knight and donned a black Jedi uniform.