Ardoise is a lightish grey / blue colour - RGGH brings out the blue IMO & Anthra is a charcoal grey which can have green or blue high lights.
Here are some pics of Anthra RH First, Ardoise RGGH City, Plomb GSH PT & Blk RH City.
I find Ardoise hops between these 1st two pics, sometimes more grey others more blue/grey.
My Anthra is SS 2010 & appears to be a straight charcoal.
I understand your 'Bal frustration', Australia has very few Bal suppliers. I hope this helps, Good luck finding your perfect grey!