Yes it’s true, because some of the the Mineral colors ( from tone 10 to tone 12 ) like all the metallic colors in the market contains an high % of ammonia in order to get the best color shadow effect, so we suggest you to start mixing the Mineral color with the developer ( the best is 3% ) 10 min. before the end of the bleaching application time in order to give time to the ammonia sent to evaporate and in order to don’t smell ammonia during the color application.
For example if you need to bleach the hair for 30 min. you have to start to mix color & developer after 20 min. and before applying it mix 1 more time.