I do color exploration all the time and pretty much all my artworks have already several color variants. I decided to go first with my all time favourite watercolor rickshaw, because surprisingly, I haven't done much in term of color variations, I could only find a mint monochrome version.
I never even thought of using the gradient tool in Photoshop to change the colors on my artwork! I do it in Procreate but it never crossed my mind to give it a go in Photoshop! I've been missing out on this one!
I tried to spot edit on the rickshaw but the colors blend a bit too much into one another for it to really work, I'll have to do it on one of my Procreate artwork where there is less blending of colors happening.