How to get this colour?

If it's dyed red, try colour removers first. You can use them up to 3 times. You can easily get that colour over a faded red though.

Can you post a picture of your hair now?

Adore Violet Gem looks like it would work well. Maybe add a touch of blue, but only a little to knock the pink back a bit.

http://www.beeunique.co.uk/index.php?main_page=product_info&cPath=151&products_id=6852
http://www.hairdyeforum.com/index.php?topic=13847.0
http://www.hairdyeforum.com/index.php?topic=13255.0

You won't get it with Wella colours i'm afraid - best checking out the links above

Oh yes, thanks I meant to mention that!

Wella does an unnatural color line also 🙂 http://w.wella.com/en-EN/color-id.aspx

That shade reminds me of what @katiesiepierski achieved recently (Timeline (5.24.14 update)) with Pravana Violet.

She mixed a few very cool-toned dyes, but hers was a bit more pinky but with a very similar iridescence as the picture you posted.  I'd bet the dyes she used, but in slightly different proportions, might give you the more purple iridescent shade... it is a gorgeous colour!

That looks spot on for adore violet gem to me!
http://www.hairdyeforum.com/index.php?topic=13847.0

http://www.hairdyeforum.com/index.php?topic=9551.0

This colour looks very similar to when i dyed over my faded Special Effects Atomic Pink with Directions Violet, which probably isn't helpful as i doubt you'll want to dye your hair first but i suspect mixing the two might have the same effect, it's thats any help at all !