reading a texture that was created via script runtime and not saved

I'm trying to save a texture that was created via script but I'm getting this error UnityException: Texture '' is not readable, the texture memory can not be accessed from scripts. You can make the texture readable in the Texture Import Settings. Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation. Any idea how to mark textures created at runtime as read / writable?