//...does that not assume a 30th october leave date though?//
No it doesn't. There is nothing in EU regulations which says what colour a country's passport must be although burgundy is recommended. Only Croatia does not follow this recommendation. In March 2019 the words "European Union" were removed from new UK passports.
As an aside, all passports worldwide are one of four colours - red, black, green or blue.
//Thank goodness my burgundy EU one doesn't expire until 2028. I don't want a little Englander blue one.//
You don't have an EU passport. What you have is one issued to citizens of the United Kingdom of Great Britain and Northern Ireland by the government of that country on behalf of Her Majesty the Queen. Apart from (inexplicably) having the words "European Union" embossed on its front cover it has nothing to do with the European Union (which does not issue ordinary passports).