I work with a very well known Java and Spring based ecommerce platform. I find that people new to the platform, regardless of Java and Spring experience, take a while to produce really good design and code.
You might know the frameworks and languages but sometimes you need experience in the specific platform.
I work in consultancy so I rarely have time to up skill someone into the platform.
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)
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!
You might know the frameworks and languages but sometimes you need experience in the specific platform.
I work in consultancy so I rarely have time to up skill someone into the platform.
Is my platform brown?