Is there a reason you are considering the integral color, rather than just primed (to be painted later)? When the siding is cut and installed, there will be areas that need to be painted anyways (to cover fastener holes and exposed ends, etc.). If you painted the siding afterwards, you would have more options for colors.

It can come colored - or just primed. If you select one of Hardie's standard colors (iron grey, night grey, or grey slate), the siding will be factory finished in that color. If you select just primed, you can paint the siding anything you want.

Yes, Hardie products are available in at least 20 colors. You should (theoretically) never have to paint the exterior.

The samples are going to be fairly accurate - as they are a factory applied color. Things always look different in the sun, so I would hold the samples up on the exterior of the house to see the true color.

We are building a house and spent a lot of time looking at houses/colors and continued to return to Iron Gray. There are a couple houses in our neighborhood with the color and we think it looks great. We're using LP Smartside so we had them do a color match to the James Hardie sample board we had. I don't think that the color looks brown or black.

It looks different in different light. I have some pics that I'll figure out how to upload.

Not sure I'd call it a true med or dark gray since but hope this helps.