Is there any point dyeing hair before a holiday?

[berri]

I usually get an all-over colour which is a few shades lighter than my usual dull brown, and every second appointment I get highlights.

So I'm due to have both this time after putting it off for ages, and the only appt I can get is the day before we go.

Is there any point? Might my highlights go a funny colour in the pool/sun? Or shall I just put up with the grey & dull brown roots which are 100% sure to be through by then, and might annoy the hell out of me once we're there?