The polymerization of your oil is what forms the seasoning layer and makes the pan non-stick. Sometimes some carbonization can occur which provides the black color. Lodge's explanation of seasoning at super high temps explains how they achieve the deep, dark black. Lighter bronze hues show that polymerization of the oil has occurred, but either wasn't cooked long enough or hot enough for much carbonization. Using an oil with a lower smoke point (like canola/Crisco) will lead to a darker color when seasoning in a home oven, though in my experience still not dark black like a Lodge.
Frankly I wouldn't be concerned about the color very much as long as you still have a layer of seasoning. Look at expensive high-end pans like Finex, Smithey, or Stargazer...they're factory pre-seasoned and all have a much lighter bronze hue than a Lodge so they don't seem to put much value into carbonization of the oil. Years and years of cooking will eventually lead to more and more carbonization as your seasoning layer builds and your pan will darken.
Since this forum loves AI so much, here's the explanation it gives about seasoning and polymerization vs. carbonization:
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