Standard grays are often the largest and has the best genes, normally. Any mutation color (as a rule) is smaller than a standard gray and the genes are a little weaker due to breeding.
Many times I have seen the runt pass the largest kit in a litter ... if it is a fighter, it will do so.
One of Gidget's kits ... the fifth one in the litter ... I had to give CPR to, ended up being the biggest of her kits. She was a real fighter, when it came time to eat. She stayed under mom constantly.
With all this being said the 84 to 105 to 150 gram spread between the three kits is sending up a flag. I would make sure the smallest one gets extra time with mom ... you may not see them fight, but if one of the larger ones put fear in it early on ... it could be still settling for "whatever is left over" rather than fight. I'd take the larger two out and let them have play time, while the little one gets to nurse for about an hour ... then the middle one back in, and last but not least, put the larger one back in with mom. I would do this several times a day. You should be able to see the smaller one begining catching up in about a week.
Also, on a more cautious note ... sometimes, if one is not developed completely or quite right, their weight seems to 'stalemate'. I would keep this little one and watch her till she is at least a year old. If there are internal problems, they should appear before the end of the first year. If it dies suddenly and with no apparent reason to do so ... you will know that there has been an internal problem from the beginning and not something you might have done wrong at the time.
Jo Ann