i only have 1 kenko nd400 filter and was thinking of getting 1 or 2 more (nd16 and 1000- i live in a tropical country), but only hoya's are available for those filters and sizes locally. know i know they are from the same company but i wanted to know if they are in face identical and am safe stacking kenkos with hoyas. the reason im wary is because a friend said his hoya nd filter gives him a warm color cast and i see my kenko filter as giving a bluish one. me or my friend could be wrong, so i wanted to ask here. i could alternatively source a kenko filter from amazon if the hoyas turn out to be 'not compatible'.