Hi Ian, It's not so much that they're blue line - I have a lot of Hataka paints, they're my main paint brand and I've been using them from pretty much day one - I still even have some pots with the original black lids before they colour coded them...
I generally use both Blue and Red line for brush painting, and both work well normally, but for some reason this particular boxing is a bit on the translucent side and the colour density is a bit low. That's not the norm in my experience - unless the formula has changed or this is an old box. They'll look okay after about four coats but it's obviously a fair bit of work on a four tone scheme to get that far, and I have a low boredom threshold lol!
Cheers!