Our Saddlebacks' vulvas turn pinky when they are in season, and yes, have a slight discharge too.
However, that's the lesser of the signs of them being in season as far as we are concerned.
It is significantly easier to tell what's going on from the front end... Frothing mouth, wild, staring eyes, chomping the bars of the gate, all dolled up with glorious mud from the wallow, sporting straw nose hair extensions, and making grunty snorty noises designed to catch the attention of any passing boar. According to my OH, it isn't only the piggies who act like that when they are in season on our farm
'Think you fancy a bit of AI, do you, Buster?!'