Google is your friend . . .
So, if you go to the Nautique website, you will see that the color is probably what they call "Mohave" or "Mohave Brown". They also have something called "Sahara Sand" that may be similar.
You can also order vinyl from Nautique (nautiqueparts.com)
Searching for vinyl that is called "Mohave" does not bring up too much, so they may have a special color, or rename a standard color for marketing purposes. their base white color is referred to as "Mistic White" might be spelled "Mystic".
You could also Google the Nautique boating forums to see if anyone as found the exact source of their vinyl. Or maybe the Natique parts folk will sell you some of their vinyl.
Nautiqueparts.com
6485 US Hwy 701 North
White Lake, NC 28337
Phone: 910-247-6201 (between 9 a.m. and 5 p.m. US Eastern Time, Monday-Friday)
Fax: 910-862-2005
Email:
support@nautiqueparts.com