Shoe polish could be used to restore it to the same colour, but not to change the colour. To change the colour of leather, requires several processes. Here is a kit that will work - http://www.furnitureclinic.co.uk/Leather_Colourant_Kit.htm
It would depend on the way the leather is finished. I have used shoe polish on leather that seems to be sealed since it has a shiny finish, and it didn't really change the color that much, but rather gave a hue/sheen of the new color. On leather that is unfinished, the item seems to absorb the color more. It never has dyed the item, but it does change the color to one that's a little deeper--kind of like oiling a baseball glove--it maintains the same color, just adds a new color overlay. I've never tried to dye a tan, unfinished purse to white or black, and am not sure how they'd turn out. I've only used cardovon on brown, or a darker brown on tan. I don't think you'd ruin anything, but you may not get the color that you want. If you don't want any particular color and are flexible, go ahead and try it.
PS: I've always used paste polish and have never tried liquid. Paste seems to cover nicks and scratches and gives a sheen when buffed. Results may vary more with liquid.
I don't know what you should use. I do know that you don't want to use shoe polish. It will rub off on your clothes.
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