Supported settings - in [] supported values

theme => theme1 [choose from theme1 to theme5]
transition => elastic [elastic,fade,none]
speed => 350
width => false
height => false
maxWidth => false
maxHeight => false
opacity => 0.85
loop => true
slideshow => false
slideshowSpeed => 2500
slideshowAuto => true
slideshowStart => 'start slideshow'
slideshowStop => 'stop slideshow'
current => 'image {current} of {total}'
previous => 'previous'
next => "next"
close => "close"
colorboxUseCss => true
colorboxUseJs => true

Example: 

[[!Gallery?
    &toPlaceholder=`gallery`
    &album=`Test`
    &plugin=`colorbox`
    &theme=`theme5`
    &transition=`fade`
    &speed = `100`
    &opacity = 0.3
    &slideshow = true
    &loop = false
]]
[[+gallery]]