If he's a really nice fish I'd go for it. In my experience spawning with a blue male and a blue female doesn't guarantee blue fry. I have a spawn at the moment where both parents were dark blue and the fry are colouring up red or blue - it sometimes on the 'grandparents' colours. You can get a really mixed batch of colours in each spawn. Be prepared though - not all males/females are compatible, raising fry can be hard work and time consuming and if you get a big spawn you could end up with hundreds of bettas, the majority males, requiring jarring from a fairly early age. I don't attempt a spawn if I don't have at least 2-3 tanks that I know will be available within about 6-7 weeks.