;+
; NAME:
;	SMEI_SEQUENCE::SET_NULL_INDEX
;
;
; PURPOSE:
;	Set the colour indices to use for missing data/out of sky.
;
;
; CATEGORY:
;	SMEI_SEQUENCE
;
;
; CALLING SEQUENCE:
;	seqref -> set_null_index, index[, /print|/screen]
;
;
; INPUTS:
;	index	byte	The colour index or indices to use. (If no key
;			is given, then it should be a 2x2-element array,
;			else a scalar)
;
; KEYWORD PARAMETERS:
;	/screen		If set, then only set the index for screen displays.
;	/print		If set, then only set the index for printouts.
;	/off_sky	If set, then set the value to use for
;			points outside the sky area
;
;
; MODIFICATION HISTORY:
;	Original: 11/7/03; SJT
;	Separate in and out of sky: 18/7/03; SJT
;-

pro smei_sequence::set_null_index, index, screen = screen, print = $
                                   print, off_sky = off_sky

if keyword_set(screen) then $
  self.null_index[keyword_set(off_sky), 0] = index $
else if keyword_set(print) then $
  self.null_index[keyword_set(off_sky), 1] = index $
else self.null_index = index

end