In "Draft" mode my error_log gives the following:

D [07/Jun/2011:01:40:53 +0200] [Job 680] File contains 1 pages
D [07/Jun/2011:01:40:53 +0200] [Job 680] Starting renderer with command: gs -dFi
rstPage=1  -q -dBATCH -dPARANOIDSAFER -dQUIET -dNOPAUSE -sDEVICE=ijs -sIjsServer
=ijs_pxljr -sDeviceManufacturer="HEWLETT-PACKARD" -sDeviceModel="hp color LaserJ
et 3550" -dDEVICEWIDTHPOINTS=595 -dDEVICEHEIGHTPOINTS=842 -dDuplex=false -r600 -
sIjsParams=Quality:Quality=1,Quality:ColorMode=2,Quality:MediaType=0,Quality:Pen
Set=2,PS:MediaPosition=7 -dIjsUseOutputFD -sOutputFile=-   /var/spool/cups/tmp/f
oomatic-3zSoAm 
D [07/Jun/2011:01:40:53 +0200] [Job 680] Starting process "kid3" (generation 1)
D [07/Jun/2011:01:40:53 +0200] [Job 680] Starting process "kid4" (generation 2)
D [07/Jun/2011:01:40:53 +0200] [Job 680] Starting process "renderer" (generation
 2)
D [07/Jun/2011:01:40:53 +0200] [Job 680] JCL: ESC%-12345X@PJL
D [07/Jun/2011:01:40:53 +0200] [Job 680] <job data> 
D [07/Jun/2011:01:40:53 +0200] [Job 680] 
D [07/Jun/2011:01:40:53 +0200] [Job 680] getting page header
D [07/Jun/2011:01:40:53 +0200] [Job 680] getting page header
D [07/Jun/2011:01:40:53 +0200] [Job 680] Received header for page 1: width 4758 
x height 6817
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: TopLeft = 0.1667x0.166
7
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: PaperSize = 8.26389x11
.6944
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: Duplex = false
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: PS:Duplex = false
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: PS:MediaPosition = 7
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: Quality:PenSet = 2
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: Quality:MediaType = 0
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: Quality:ColorMode = 2
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: Quality:Quality = 1
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: DeviceModel = hp color LaserJet 3550
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: DeviceManufacturer = HEWLETT-PACKARD
D [07/Jun/2011:01:40:53 +0200] [Job 680] % IJS parameter: OutputFD = 10
D [07/Jun/2011:01:40:53 +0200] [Job 680] PaperSize = 8.26389x11.6944
D [07/Jun/2011:01:40:53 +0200] [Job 680] Dpi not set, using default (600)
D [07/Jun/2011:01:40:53 +0200] [Job 680] PaperType not set, using default Normal (0)
D [07/Jun/2011:01:40:53 +0200] [Job 680] Copies not set, using default (1)
D [07/Jun/2011:01:40:53 +0200] [Job 680] Tumble not set, using default Off (0)
D [07/Jun/2011:01:40:53 +0200] [Job 680] Quality: Medium
D [07/Jun/2011:01:40:53 +0200] [Job 680] Bitmap size 4768x6912 (7.94667x11.52 in)
D [07/Jun/2011:01:40:53 +0200] [Job 680] Unsupported color conversion request
D [07/Jun/2011:01:40:53 +0200] [Job 680] GPL Ghostscript 9.02: Unrecoverable error, exit code 1
D [07/Jun/2011:01:40:53 +0200] [Job 680] renderer exited with status 1
D [07/Jun/2011:01:40:53 +0200] [Job 680] Possible error on renderer command line or PostScript error. Check options.Kid3 exit status: 3

Near the end of this snippet it says "Unsupported color conversion request" and Ghostscript aborts.

It seems that in draft and normal mode the driver requests color spaces which Ghostscript cannot supply.