You could solve this fairly easily by giving an LLM the json definition of your sublime text theme and just transforming it onto a zed spec theme? No need for screenshots.
Interesting - now that I think about it, feeding Claude my particular Xcode theme from VS code to replicate in Zed, the color tones were quite far off how it looked in cursor. I don't know enough about color rendering to know why that is, but I feel you!