If it's polished aluminum, you can scuff it with a brillo, use a self etching primer, and paint it.
I have the aluminum step tread rockers and corners on my CJ, once the polished look didn't look so good, I did the above, and painted them gloss black.
The paint has held up great.
Corner before (it's dirty, and the rocker is off the Jeep in this shot)
Corner after paint: