;+
; NAME:
;	SMEI_SEQUENCE::GET_NULL_INDEX
;
;
; PURPOSE:
;	Return the colour index to use for pixels with no data.
;
;
; CATEGORY:
;	SMEI_SEQUENCE
;
;
; CALLING SEQUENCE:
;	index = seqref -> get_null_index([/print|/screen])
;
;
; KEYWORD PARAMETERS:
;	/print		If set, then return the colour index to use for
;			printed output
;	/screen		If set, then return the colour index to use for screen
;			displays. (This is the default).
;	/off_sky	If set, then return the value to use for
;			points outside the sky area
;
;
; OUTPUTS:
;	index	byte	The colour index to use.
;
;
; MODIFICATION HISTORY:
;	Original: 11/7/03; SJT
;	Separate in and out of sky: 18/7/03; SJT
;-

function smei_sequence::get_null_index, print = print, screen = $
                                        screen, off_sky = off_sky

if keyword_set(print) and keyword_set(screen) then $
  smei_msg, /warn, ["You've asked for both print and screen indices", $
                    "Returning print"]

if keyword_set(print) then return, self.null_index[keyword_set(off_sky), 1]
return, self.null_index[keyword_set(off_sky), 0]

end