Does it matter whether you write "картини мають," or "у картин є"? Is one more proper than the other? In Russian, we're told to use "у неё есть" rather than "она имеет," because the first one is more proper speech.
You could also say "У її картин завжди теплі кольори" without changing the meaning. Both variants are correct and sound absolutely fine.
In Ukrainian you can say "Маєш хвилинку?" ("Got a minute?"), which is a common colloquial phrase. You can also say "Є хвилинка?" (short for "У тебе є хвилинка?").