Can I spray paint a metal swivel bar stool?
from brown to black.
or brown to white?
if so what is the best pain to use?
here are some similar
http://www.google.com/imgres?q=metal+swivel+bar+stool&hl=en&tbo=d&tbm=isch&tbnid=BTo6LebWahqy2M:&imgrefurl=http://davinong.com/design/8206/bronze-finish-adjustable-metal-swivel-counter-height-bar-stools-set-of-2&docid=CFFqLXPbrai9DM&imgurl=http://assets.davinong.com/images/entry/2011/08/18/8206/cheap-bar-stools.jpg&w=800&h=800&ei=5YP3UI36Eoqo9gTw2oGYAw&zoom=1&iact=hc&vpx=856&vpy=255&dur=1978&hovh=225&hovw=225&tx=130&ty=91&sig=107914970903705245704&page=1&tbnh=139&tbnw=139&start=0&ndsp=37&ved=1t:429,r:16,s:0,i:132&biw=1280&bih=702

Spray paint for artists is definitely worth a look as well. A lot more colour options and has been designed to be long lasting and often use better pigments than those you find in DIY shops. Cheaper as well.
Have a look at Molotow Premium – http://www.writersbench.co.uk/spray-paint/molotow-premium-belton.aspx
Use thin coats and layer it up so as to avoid drips, and finish off with a clear coat varnish to protect it. Something like – http://www.writersbench.co.uk/spray-paint/montana-industrial-matt-varnish.aspx
Krylon makes spray paint specifically for metal.
Yes. Any high quality spray paint for metal will work, however, if the existing finish is plated, i.e. chrome, brass, etc., you will want to use a self-etching primer before you apply the paint.