Colour gradient like photoshop

Hello,

Probably, most of this difference is because you selected wrong colors:

  1. The pink is not (0.835, 0.00955, 0.538) but something like (0.922, 0, 1).
  2. The green is not (0, 0.561, 0.08648) but (0, 1, 0.00913).

My values are not perfect too but much closer to the PS, because I used the color picker:

Also keep in mind that the preview scene is not a Texture/Image, it is a scene, it has a light etc and this changes the final preview result. Press L and Left Mouse Button to see how light direction is affecting the result.