PRO blacktop
;+
; NAME:
;	BLACKTOP
; PURPOSE:
;	Making the top of the colour table black.
; CATEGORY:
;
; CALLING SEQUENCE:
;	BLACKTOP
; INPUTS:
;	None.
; OPTIONAL INPUTS:
;	None.
; KEYWORD PARAMETERS:
;	None.
; OUTPUTS:
;	None.
; OPTIONAL OUTPUTS:
;	None.
; COMMON BLOCKS:
;	None.
; SIDE EFFECTS:
;	The highest colour in the colour table is changed to black.
; RESTRICTIONS:
;	None.
; PROCEDURE:
;       The presently-loaded colour table is read into arrays for
;       the red, green, and blue components.  The last element in
;       each array is set to 255B, and the colour table is loaded
;	from the modified arrays.
; EXAMPLE:
;	loadct,13	; Load the RAINBOW colour table
;	blacktop	; change the last colour from red to black
; SEE ALSO:
;	WHITETOP.PRO, WHITEBOT.PRO
; MODIFICATION HISTORY:
; 	Written by:	DPS, ISR, 950531
;-

TVLCT,r,g,b,/GET
n=N_ELEMENTS(r)
r(n-1)=0B
g(n-1)=0B
b(n-1)=0B
TVLCT,r,g,b

RETURN
END