Vulkan is colorspace agnostic. Though at some point before the bits are converted to photons, the colorspace must become known. That's why it is asked for in the swapchain creation.
imageFormat specifies what the image format is (same as it does in vkCreateImage()). imageColorSpace is how the swapchain\display interprets the values when the image is presented.
So if you have UNORM, that means unspecified color space, and they are good ol' raw bits. Or rather it means that you are in charge of the color space (if the image even stores color, and not something else entirely). If you use VK_COLOR_SPACE_SRGB_NONLINEAR_KHR with *_UNORM, it means the swapchain takes your bits and it is gonna assume it is already SRGB when presented. If it is *_SRGB, then that is no different for the swapchain itself, but what happens is that the created VkImages are *_SRGB format, which means when you use them then the color is being linearized for you (same as would happen if you created a non-swapchain VkImage).