This may help.
Had a similar issue with trying to refurb a very badly stained dingy last year which also had some repairs in new / off colour patches - nice.
Resolved the best product was to use a printers ink which was sovent based and would after thorough cleaning adhere to the pvc. It worked very well and proved servicable.
You need to carefully check what your cover is made from first and perhaps try a sample section. It is very dear but the coverage is enormous as it is very thin and very strong - wear gloves etc. and mask up everywhere as it runs like hell and will stain everything it touches !
There are specialist suppliers for these printing inks who have many different types / solvents etc. in about 20,000 + colours.
I found after telephoning that a personal visit is required so suggest you find one local to you or ask a printer where to go.
before you replace it, consider proper cleaning with detergent and steam - the same technique as cleaning tubes can be used... to see the results have a look at http://www.bluesheets.co.uk/wordpress/index.php
see "the futures bright" for pictures
