I need to cover or disquise a big cold air return

Here's some good ideas.

https://www.pinterest.com/pin/367747125796311499/?lp=true

Anything you use to cover a cold air return will negatively impact its ability to perform its primary function. Don't know why you would need to do this. Is it damaged in some way that makes it unattractive? Is there some specific high-end decorating scheme that makes the appearance so undesirable that it absolutely must be hidden? It would be possible to build a grill, but it will stand out from the wall or floor so a lot depends on the context of the location of the return.

it’s called a return for a reason, your hvac needs both vents and returns to function properly, so don’t cover..if you put something in front of it, leave at least 6” gap clearance.

Spray paint it to match your wall color.

Disguise it. Don't cover it like DW says.

you cannot cover it, if there is a removable vent paint it

SOME SORT OF RECLAIMED METAL GRILLWORK.