Black or silver .... The color is your choice. Just make sure it is aluminum and not the nylon type. Bugs will eventually eat through the nylon. You should be able to find at any hardware store.
You were soooo lucky... It only takes a couple of moments or a simple distraction to lose a chameleon. Personally I use a caging system that a friend made out wire screen and conduit piping. Its a block of 16 cages on caster for when I put them outside.
First welcome to the forum and your new addiction. Given the choice I would go with the older chameleon. Assuming that it is of good health. A well established older chameleon will have a greater survival rate and have a bit more allowance for mistakes during your learning curve.