Only thing that 'matters' is that the tank, the piping, etc. are 'rated' for potable water. This will insure a low level of 'extractables'. ABS and polyethylene are available in 'rated for potable water usage', the 'plain-vanilla' stuff usually isnt.
Polyethylene is the usual choice because of inherent 'chemical compatibility' to sanitizing chemicals, and 'smoothness' hence 'clean-ability'.

Clear or opaque doesnt matter as bacteria and fungals, etc. *are going to grow* if you dont 'dose' with chlorine, etc.