The v1a and 1b exist in a dark grey / black. This can appear with and without the circle. Obviously it does have a thin or fat dent though, but I'm led to believe that because of wear in the mould it is possible that the dent can be accentuated or decentuated.
Since both the 1a and 1b exist in dark grey / black it is also possible that the 1c could exist in the same dark grey / black, although TIG have not documented one.
Until recently I had a v1 blaster that I could not 100% determine if it was a 1a, 1b or 1c. It could well fit your description. It was definitely grey and not solid black, or blue / black. Pictures attached.
In the end I decided it was a 1a fat dent but the dent was not very distinct, appearing like a 1c. Unfortunately it has been sold so I can not reassess it. See what you think.