Here's Romantika. It's actually a bit darker than the upper flowers, more like the lower ones - just overexposed photo.

Below is Viola which I think is actually just a bit darker, though they aren't near enough so I can compare colors in person. I like the flower form a bit more as well since Romantika's tepals curl back as the flower ages. It's a bit less red as well, more a true purple, while in my garden R. has a definite red-purple tone. The flowers over toward the left side are more true to color while the one in the center is overexposed.

I don't have and haven't seen Shogun.

Remember that besides the question of your computer's color balance which may effect how you see the flower color, your soil and sun exposure may effect how the colors look as well.

Shogun clematis is extremely hard to find now - and it's a very, very dark blue as you can see in the photo.