An example of a framework with assets. https://medium.com/better-programming/ios-build-your-cocoapods-framework-with-an-example-app-from-scratch-fd0f7bdf3f8c

HelloWorld.swift

public class HelloWorld {
    let greet = "Hello"

    public init() {}

    public func hello(to whom: String) -> String {
        return "\(greet) \(whom)"
    }
    
    public var helloColor: UIColor? {
        if #available(iOS 11.0, *) {
            return UIColor(named: "HelloColor", in: Bundle(for: HelloWorld.self), compatibleWith: nil)
        } else {
            return nil
        }
    }
}