One of the most common reasons that blue dye stains leather is bleed from the indigo usually used to dye denim in. Some denim, no matter how much you wash it, continues to bleed on objects and surfaces that rub against it. The treatment for removing blue dye stains from leather, regardless of the reason, is the same. Patience is the key to removing blue dye.
Add clear liquid dish soap to a bowl of water. Mix well.
Dampen a cloth with the sudsy water mixture.
Rub the stain with your dampened cloth. As stain transfers onto the cloth from the leather, use different, fresh sections.
Rinse and wring out the cloth so that there is no soap left on it.
Wipe the remaining soap off the surface of the leather with your cloth.
Warm water works better than cold water for removing the stains.
Don't scrub the leather hard with the dampened cloth. Instead, use short, vigorous medium weight strokes.