get category by id

hello,

something apparently simple ; I am looking for the category of an events (in php)

I have my function which receives the event_id… but how can I get the event category name ?

function get_color ( $id ) {

switch $category
categ1 : $clor=blue
categ2 : $clor=red
categ3 : $clor=pink
blablabla

}

Cheers
Alexandra