I always believe it's a good idea to have a few years in hand prior to the expiry date.
I wouldn't be surprised if the Passport Office may get inundated post Brexit. People wanting rid of their Red European models. :-)
If you have no plans to travel just do it in your own time. I was reading that there is a chance they won't carry months over onto your new one post Brexit and you'll need 6 months left on your passport for all travel. But obviously that doesn't apply to you.
That means if your passport needs three months on it after Brexit, you'll have to renew three months early and it won't be credited, so you get a 9 years 9 months passport for your money.
I would renew it now, it only has a few months to run, not sure if your new passport will start from application date or from when your current one expires.
Colour of cover is irrelevant IMO unless you have more money than sense.
Although you may have no plans to travel, passport is one of the best forms of ID you can have.
I would never leave it this late before renewing but having been widowed and moving within the last couple of years it has been overlooked. Only noticed as I had to show my passport at the bank for ID. Probably will do it soon whilst I remember as might go away next year.
I've just re-newed mine. It came on Wednesday. My old one didn't expire till May 2020, but having booked a foreign holiday for March 2020, I decided to do it now rather than later. No other consideration really. Not bothered about a blue/red one as long as I'm ok to travel.
Why is Brexit an issue? Apart from the colour and the removal of the words "European Union" from a passport it will be no different to one issued pre-Brexit.