Hello prashath,
give an example to identify color, but it only recognize colors mentioned in the story only.
This might be because you don’t provide enough data/example (different colors) in your nlu.md. I have faced similar situation before and after providing a sufficient amount of example, the bot can pick up entities which are not in stories.
for a scenario like credit card balance, we cant add all the possible numbers even though we can for colors, how can we remember numbers?
You can do the same as i said above plus using regex features in addition. You can read about Regex features here: NLU Training Data
Those are my experience after working with identifying date entities.