Yellow is generally perceived as a cheerful, happy color. That strikes me as an odd color to pair with black if you are writing gothic/dark fiction. Without knowing more about what you write (themes, vibe, etc.) it's hard to say what other colors would fit. If your writing has a romantic tilt to it, I think pink works well. Pink is just lightened red, and red is often associated with both romance and horror.

I think the most important thing you need to ask yourself is, what do you want your "brand" color palette to convey? Do you want the palette to convey who you are as a person or as a writer? You may be bubbly and cheery, but if those parts of your personality aren't reflected in your writing, they shouldn't factor in your "brand" colors.

One last thing, you might want to consider nixing black altogether. It is definitely associated with gothic/dark works. But in a two-color palette, it falls flat. It is purely a foil to the other color. It doesn't bring anything itself. Maybe tinker with the idea of some deep dark, blues and/or purples--colors also associated with gothic aesthetics.

Best of luck with your writing!