IIRC, a 90 or 91 Syncro base model was available in Pastle White or Flash Silver.
The Westy Syncros of those years were available in Pastle White, Flash Silver, Orly Blue and Bordeaux
Red.
The 90 and 90 Carat was available in Tornado Red.

Vanagon.com, search by year under the info section:

Colors available
Pastel White  Flash Silver Metallic  Orly Blue Metallic  
>Bordeaux Red Pearl Metallic  Tornado Red  
>(Not all colors available on all models.) 
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________________________________
From: Jeff Lincoln <magikvw@GMAIL.COM>
To: vanagon@GERRY.VANAGON.COM
Sent: Tue, January 12, 2010 9:52:04 AM
Subject: Re: FS: '90 wolfsburg Syncro TDI

This may seem crazy but bear with me because I am extremely color blind.

However, is there a possiblity that it is Orly blue and appears purple in th
pictures for one reason or another? My bus is Orly blue and I've been told
in certain lighting and such it looks purple.

Again just a theory considering that I couldn't tell you if the bus in
question is purple or not - looked Blue to me :)

--
Thanks,

Jeff
'90 Carat (Grover)
'86 (We call this one Parts)
'78 Bus (Melissa) Patty's Bus