That depends ☺. But “pink-colored” reflects the structure of “roz-koloraj” while “colored pink” does not.
In the first expression “colored” is only formally passive, meaning just “having the color [pink]” while in the second it is a true passive, implying that somebody actively colored the flowers.
(I intended to include a Union Jack character after the smiley but Duolingo reacted by trashing the whole rest of my post. So be careful with Unicode characters > 65534.)