Thanks for all your 'tea staining tips' (PG Tips ?...HaHa) I did take the advice given and dunked the bow fender in a cup of hot water a tea bag and left it for 20 minutes.
I hung it to dry on the washing line (I won't tell you what my wife commented 😳).
When dry it's clearly taken a nice shade of light brown and I'm happy with the result.
The photo is the one on the bow of my crash tender and the the 'stained' one for comparison.
I'll probably stain the crash tender one too.