another cup of tea

another cup of tea (altogether) — совсем другое дело, совсем из другой оперы, это две большие разницы.

Example 1: Web-mastering doesn't relate to programming. It's quite another cup of tea. — Создание веб-страничек не связано с программированием. Это совершенно другое.

Example 2: Recreational sport is relaxing. Professional sport is another cup of tea altogether.

see also
[different kettle of fish]
another pair of shoes

(a) horse of another color and a horse of a different color (another matter altogether)

Example 1: I was talking about trees, not bushes. Bushes are a horse of another color. (thefreedictionary.com)

Example 2: Gambling is not the same as investing in the stock market. It's a horse of a different color. (thefreedictionary.com)