You might want to got a little finer on the polish. At least 320,,perhaps 400. The rougher polish will show more of a black color than a blue in my experience.
I use MarkLee and get a nice blue color that way.
Also Laurel Mtn if I do a cold rust process. It's a little agressive at times so you have to watch it closely that it doesn't etch the surface too much. Then you're right back to the matted surface and a black color again.