Can I turn idexed colors palette into gradient map presset to turn something grayscale back to col?

For example I have 100 colors indexed image.  I turn it into grayscale , then RGB and now want to make it  color again by applying  a gradient  in gradient map adjustment layer .   I perhaps could tediosly make it on my eye of course but  is there an automatted process for that  or perhaps somebody could write a script that could turn those 100 indexes from an image palette  into a gradient map?

Perhaps a way to turn saved color table  in a color gradient working over same image with  applied default grayscale color table ?