If you are filing a logo in the European Union, filing in black and white will not allow you to use your logo in any color, unlike the US and Canada. Marks that are registered in black and white but used in color may be vulnerable to cancellation if the owner of the trademark does not prove genuine use of the trademark “as registered”. It means that the logo trademark has to be filed in the color that it will be used (and not in black and white unless the owner plans to use the logo in black and white).
Full rules with detailed questions and answers can be reviewed here: European Common Practice.
If you are thinking of filing a new trademark application, you may want to file two applications: one in black and white to cover all color combinations if you ever need to bring a proceeding before a National Court that has not implemented European Common Practice and one in a particular color that you use to comply with European Common Practice. As us about a special discount for a black and white and color logo (if filed at the same time).
To open in a new tab, click: In what color should you file your logo in the European Union?