In the side bar it says that you get the none coloured effects of purple nodes whether you take it as a red or a blue node. So for Sextual Energy/Dominance it makes sense to me that if you take it as a red node you get the none coloured effects (the reduction in spell cost) and the red effect (nothing) so taking it as a red node just gives you the cost reduction. Taking them as a blue node still gives the neutral cost reduction effects but also the blue restriction to casting spells. Or you can take it as both a red and blue node to reduce your costs by twice as much while still having the blue restriction. Also note that the formatting would allow for a purple node to have a none coloured effect a red effect and a blue effect that option just wasn't used in this particular case.