Jack Frost is a medium blue color with heavy shading, some subtle silver sheen and heavy purple/red sheen. Any nib medium and up will clearly bring out the sheen. The color itself reminds me of a bright, cold winter day. I wouldn't use it in the office, but it is not wildly inappropriate.
The ink behaves really well. There is no feathering on this paper, high shading, a lot of sheen, and some shimmer as mentioned. The Splatter makes it visible. Jack Frost is not too wet but has average drying times, writes smooth enough and with negligible show-through. The ink probably likes ice more than water, it immediately smears, even days after writing.
For this review I used ClaireFontaine paper.
The color itself reminded me of a dark Kyanite du Nepal (Herbin) or Kon Peki (Iroshizuku). Sumor (Sailor Manyo) is a lot lighter.
There is one thing about the bottle(s) that should be mentioned. The caps are virtually impossible to screw back on straight. They have the propensity to cross thread. Not just on this bottle but on the other two colors I bought as well. A pity.
All in all this is a very beautiful color. Highly recommended!