1) It’s a grammar construction shi……de, ‘de’ is added at the end for more emphasis, without it, you can say either: zhege dongxi shenme yanse? or zhege dongxi shi shenme yanse, both will be perfectly fine.
It’s more common to use ‘de’ in answering, e.g. hong2se4 de chen4shan1-red shirt, instead of hongse chenshan or hong chenshan. Because ‘de’ is commonly added after adjectives. However, the latter two are also perfectly right.
So that’s why it’s better if you ask: zhe4 jian4(measure word) chen4shan1 shi4 shenme yanse de? And answer: shi4 hong2se4 de, or the full sentence: zhe jian chenshan shi hongse de.
However, it’s wrong if someone asks: zhe jian chenshan shi shenme yanse, and you answer: shi hongse, or zhe jian chenshan shi hongse. The ‘de’ at the end here must be added. Otherwise, shi hongse will mean “it’s red, it’s colour red”, ‘red’ here is not an adjective.

The only other way of saying this example without ‘de’ will be zhe jian shi hongse(de) chenshan.(with or without ‘de’ both ok) But, the logical stress is kind of different here. It stresses more the word chenshan(shirt) here, not it’s colour.

Hope you can make some conclusions out of this.

2)juhuangse and chengse both fine, I think, juhuangse is used more in Taiwan and chengse in Mainland China, otherwise exactly the same.

Best,
Serge

Can you explain the deal with “de” being used with colors?

“Zhe ge dongxi shi shenme yanse de”

Why not just “Zhe ge dongxi shi shenme yanse”

Also, you have 橘黃色 for orange. I’ve seen it elsewhere as 橙色. Are they simply synonyms? If so, which is more commonly used?

Thanks a lot.

Steven

keep up the good work

Lars