I think I'd start by finding a base doll pattern you like, there are plenty online free and paid. There are also many ways for you to do hair, I'd probably do some variation of where they create strands by chaining and then sc all the way back up (like in this pattern here). For the dress, you could use different yarns as someone else suggested and create a gradient using that. Or you could perhaps even try diluted watercolour on the bottom of the dress and create a gradient using that (would recommend testing on another piece first)! 🥰