I happened to have these three similar coloured inks so I did a quick comparison showing you some writing samples, sheen shots, and colour density. I hope it is helpful.
1. Sky High and Souten are very similar in regular writing, but I can see more reddish dye in Sky High which shows up as more sheen.
2. Sky High and Souten flows from the nib just about the same.
3. Kon-Peki is slightly greener than the other two, leaning more cerulean in colour. Difference is noticeable in regular writing.
4. Kon-Peki feels more fluid/watery coming out of the nib. As it is an Iroshizuku ink, known for their extraordinary flow characteristics, I consider it in line with other Iro inks in the great flow. This doesn't mean the two sailor inks (Sky High and Souten) are less flowy, they are well lubricated and has good flow but it's just that Kon-peki has more watery flow.
Now on to the photos:
Writing sample shows Kon-peki is lighter and slightly greener in colour.
Writing sample from a different angle.
Painted with watercolour brush, thin lines, thick lines, and words with flexy nib.
2 drops of ink from syringe spread out with blunt needle to roughly 2.5cm (1 inch) diameter. Words are in Noodler's Bulletproof Black. Photo is taken straight on.
Same as above, but photo is taken from shallower angle to enhance the appearance of sheen.