Not a big fan of those holes... so I purchased the gutter guards... installed them after I painted black the vents/holes/grills/whatever.
The black was an improvement but, as other have said... the paint starts to chip. Now... the silver guards look(ed) great behind the painted black. However, I wasn't going to remove the bumper cover everytime the black paint chipped. What I did was tape around the vents/holes/grills/whatever... paper it up to avoid overspray... and touched up the paint. NOT removing the bumper cover means that the shiny silver gutter guards now match the paint of the vents/holes/grills/whatever. All good.
I do a touch up every few months, or whenever the chipping gets out of hand.