I'd suggest either using a separator other than ':', or referencing it with $chr(58).
$iif($($+(%,some,$chr(58),var),2) == 1,$style(1)) Set:set %some:var 1
$iif( [ [ $+(%,some,$chr(58),var) ] ] == 1,$style(1)) Set:set %some:var 1
$iif( %some [ $+ [ $chr(58) ] $+ ] var == 1,$style(1)) Set:set %some:var 1
