Yes it is normal that there is a stain on the bulb(s). What you don't want to see on the bulbs is a really dark smoky grey or black color. As soon as the bulb turns opaque then it is time to email us or call to get a replacement.
Did i read that last part correct about using HID's for inside lighting? Like in your house or office? I took one of our testing stations home and was using it for s&g to see the difference, i thought i was the only one that did that. I thought it was too bright though and found myself looking at the bulb like a bug flying into the bug zapper and saw sun spots for a while so had turn it off. Pretty funny though hearing someone else used it at home.