Opaque black is best, you can’t see biofilm inside and lack of light prevents algae from growing. Don’t want to see hoses coming up behind tank, well you should have a opaque background on tank anyway. Doesn’t matter what color it is, get some .125” pvc and some spray paints and do a gradient fade of any color you like.
Only part of return or intake for canister you should see is what comes over the tank rim inside tank. Sorry but these but these clear glass pipes on clear glass on back look like crap after only 2weeks, who wants to have to clean inside of their aquarium plumbing every 2 weeks to keep it looking good. Cleaning inside aquarium is time consuming enough.
I really wish they would take those stainless attachments and lengthen the downpipes so all you can see behind tank is a stainless pipe behind clear glass, I like those stainless attachments look a lot.. Probably a little smooth flow S elbow as it crosses stand level. All you would see through back glass is a opaque piece of stainless tubing, not the crud growing inside of it. Of coarse being opaque stainless there would be way less algae/crud growing in tube to begin with.
There I’ve finished my rant, glass pipes are the devil and meant for narcissistic posers. :-)