Permanently failing to build

[A13xCode]

Put simply, the project (DesignableXTesting) doesn't build and all custom objects remain normal. I was browsing it to see what I could do with these Designables, but it won't build. No errors, no nothing. I click refresh all views and it just fails. Why?

[mjmoeykens]

@A13xCode, this is strange. I opened the project and was able to build and run it in Simulator. I updated the project for Xcode 9.3. Try it again and see if it works.

[anudeep94]

i got the same issue Designable Build Failed while building the project, in Xcode 9.3.
The Warning message was " Base.lproj/Main.storyboard: warning: IB Designables: Ignoring user defined runtime attribute for key path "firstColor" on instance of "UIView". Hit an exception when attempting to set its value: [<UIView 0x7fce7b517d40> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key firstColor."

but when you run it on simulator for some views it works, for others it doesn't apply.
I was using the gradient for the views in my project.