'' RED'' Swallow

Yesterday whilst in and around crow Hill I noticed a large number of swifts heading north with a few swallows in with them also heading north one Swallow stood out a  beautiful-looking bird, with underparts and under-wing coverts a wholly deep-reddish colour, the red extended to the under tail coverts and made for quite a striking bird. I watched it for about 10 mins hunting insects low amongst the juncuss and around the manure piles ,it then headed off low n/w and was not seen again.Anyone else noticed one of these before.??