That sounds like the platform is relatively complex. I've seen Java/JavaEE/Spring code where it was easy to get started, since the platform was built as simple as possible. I've also seen Big Balls of Mud where a developer needed months to be somewhat productive. So the question shouldn't be: "Is my platform brown?" But rather: "Have you ever worked on a freaking castle with hundreds of secret passages?".

Sometimes complexity is unavoidable. The interviewer may ask a question like: "What are your experiences with complex code/legacy code?" (If the interviewer is able to accept the reality of course)

No, you need a cooper. Making watertight barrels is really hard, a house builder can make great houses, but probably crappy barrels.

I wouldn't say that was brown exactly, but I know exactly what you mean with big ecommerce platforms and all kinds of other vertical-market software. It can take months or even years to learn all of the tricks.

That being said, it is always a gamble. A great programmer might pay off in the long run more than a mediocre programmer who already knows the platform... or not!

No brown is the colour the wood was painted afterwards. In the context of this story, I'd say your platform is walnut.