the colour is a color 8)

file:///home/opt/processing-1.0.9/reference/color_datatype.html

(edit: oops, link to my local copy of file - am used to the library link being available at top of page but it's not there anymore so i used my bookmark to local copy. anyway, see cedric's links below)

its of the datatype color
http://processing.org/reference/color_datatype.html
http://processing.org/reference/color_.html

to change from RGB to HSB you have to use colorMode
http://processing.org/reference/colorMode_.html