I found out about a hybrid pen called the Uni-ball Jetstream, "An affordable pen that writes incredibly" at http://thewirecutter.com/reviews/the-best-pen/ and would like to add my observations.
They only mention in passing the BLX models, but I would like to highlight them here.
The idea is that black ink is mixed with color, and I like the effect. It is somehow subtle yet bold. I've always preferred blue-black ink to pure blue anyway. As of this writing in August 2017, it just so happens that on Amazon, the 5-pack of different colors is actually cheaper per-pen than the 12-pack of any single color.