How do I create this kind of gradient design?

[hadicanç3530126]

I want to try a design idea similar to this but couldn't figure out how to create lines with these gradient colors. 

[lambiloon]

Hi are you working in Photoshop ?

[hadicanç3530126]

Hi, thanks for the reply! I tried Illustrator first - the blend tool- but couldn't manage the create a similar thing. Now I'm trying on Photoshop. I'm open to try anything on both Photoshop and Illustrator. 

[Semaphoric]

You could add a Gradient adjustment layer, and draw your line on the layer mask. You could then manipulate that.

[Chuck Uebele]

I'm not really sure what you mean by lines. Are you talking about the soft curved line, at the top of the gradient? If so, the only way I know is to create a mask and paint out the areas you don't want.

[c.pfaffenbichler]

Painting the black (or a Layer Mask) may be unavoidable, but a shape with some Smart Filters might help to get a start.