Generally, silicone- like Armor-All is a good treatment for weathered vinyl, after a good scrub cleaning. I have used chlorine-containing cleaners (like spray tile cleaner) and a brush with good effect but followed by a good rinse as chlorine staying on wouldn't be good.
Some have cautioned that silicone makes the tramp slippery but my initial applications were just absorbed and I haven't got to a slippery point yet.
There are advertised vinyl dyes and paints, mostly used for auto renovation, but I haven't tried those yet as the 'natural' faded blue tramp seems a good color.
I'm definitely thinking that a tramp cover will pay benefits as the local birds seem to become incontinent as soon as I scrub the tramp
