Sometimes it depends on the labeling
Blue Reef Chromis (Chromis cyaneus) &
Blue Chromis, Green Chromis or Blue/Green Chromis(Chromis viridis)are all peacful.
However,
Blue Damsilfish or sometimes also sole as Blue Chromis(Abudefduf cyaneus or Chrysiptera cyanea) are agressive.
Check the scientific name if in doubt about what your getting. But most Blue Chromis and Green Chromis are basicly the same animal different color and Blue Reef Chromis are just as peacful as the Blue/Green Chromis.
The difference is when some sell Blue Damsels under the name Blue Chromis.