Any method to create a watercolor effect on a gradient ?

[Luzarin]

Currently, I have a circle with a rainbow gradient. However, I want to make the rainbow colors have something like a watercolor effect as well.

Is it possible ?

I thought of airbrushing, but it doesn't work as I can't airbrush with the exact color as the rainbow gradient I have used.

Thanks in advance

 

[RTContent]

There is a watercolor filter. Filter - Artistic - Watercolor.