Pilot Hi-Tec-C 0.4mm Sear Blue
This shade is one of my favorite blue shades. It's a bit light, but not too light to read. here is a picture with it next to Blue and Light Blue :

and here is a comparison to other Hi-Tec-C 0.4mm blue shades(and black):

Pilot Hi-Tec-C 0.4mm Lavender
This shade is a bit softer than the regular violet, I actually like it better - and it also works nice with other purples and pinks. Here are some text samples so you can see what I mean.

 

Pilot Hi-Tec-C Blue-Black 0.4mm

This pen writes smoothly, no stutters or dry-ups (I've been using it for about a year)
This color could be an in interesting replacement for black, when black is too "serious".
Here are some pictures, which are the most important part, right?

Piolt Hi-Tec-C Slim Knock 0.4mm Blue and Blue-Black

I ordered these pens from Ebay about 8 months ago, I wanted to try this version of the Hi-Tec-C pens, and found out it's got some advantages and some disadvantages.
to make it simple:

Advantages:
1. Suits right in my notepad.
2. Writes smoothly (just as it should).

Disadvantages:
1. A bit too small, my husband for example did not feel comfortable using it.
2. The ink barrel is significantly smaller than the regular Hi-Tec-C pen.

a Hi-Tec-C on the left,
next to the Slim-Knock Hi-Tec-C on the Right.

Here I took apart the Slim Knock on the bottom,
and above - the regular Hi-Tec-C.