The hi-vis stakes in the BPL shop are not anodized, but actually somehow "painted".
Unlike aluminium, the color of anodized titanium is caused by interference of light on surface layer of titanium oxide. This layer is created by the anodic oxidation in an electrolytic cell. For more info, see:
or google it yourself.
I've tried the process at home with success, but unfortunalely I can't go to the higher voltages to get brighter colors... I was surprised how easy it was.
The coating on the stakes is, in my opinion, some sort of industrial painting, probably hardened at high temperature (like the powder coatings used on cars, bicycles...)
If you're not a perfectionist, the easiest way to make them more visible is to wrap the hook of the stake with a bright-colored tape, or attach a short loop made of hi-vis string/webbing/fabrics. And what about a retroreflexive tape to make it shine in the dark?