Anele: Why don't you post on the HD forum. I bet you'll get a lot of help and more suggestions than you probably want. I would be very tempted to take the whole thing down and give yourself the fireplace that you want. Lighter grout IMO will only enhance the dowdiness of the brick and that itty bitty hearth. If your husband is right, you might find some very nice brick beneath.

There are thousands of things you could do with that to improve it, lightening the mortar isn't one of them. I agree you will get more advice on the decorating forum.

I would start the change with a sledge hammer, good luck.