Help with raw shrimp color

I usually slit the prawn flesh just above and along the line of the vein to expose it and to make it easier to then pull out.

This is different from butterflying a prawn, which involves a deeper cut (but not all the way through) of the prawn along most of its length along the same line as the de-veining cut, but also leaving the tail on usually.

This video shows the de-veining technique and the butterflying.

I was always taught to take the head and tail between your fingers of each hand, pull it out straight, push together slightly, then pull apart. That should pull the whole carapace back off the body. Then you can pull off the head (and legs if they're still there) and you're done.

However, I've seldom gotten it to work when raw, and less so when cooked.

I agree, cooked shrimp are harder to peel, and just add an unwanted challenge to the diner when included in most dishes.