Any brightly coloured background is a bad UI, for physical and physiological reasons which I expanded on in this answer Should software for 8 to 14 year olds be colourful and "childish"?

As for how to draw attention to an error message against a pink background: you need to increase the contrast between the red background and the pink background. In @DA01's example above, a white or black border around the red panel containing the error message would help.

But the real problem for me is the bright pink background. Work around it if it's a given that you cannot change, but do not be responsible for choosing it. Pink or red is particularly bad as a background, because chromatic aberration in an eye always forces it forwards from the plane of a neutral screen.

Any brightly coloured background is a bad UI, for physical and physiological reasons which I expanded on in this answer Should software for 8 to 14 year olds be colourful and "childish"?

As for how to draw attention to an error message against a pink background: you need to increase the contrast between the red background and the pink background. In @DA01's example above, a white or black border around the red panel containing the error message would help.

But the real problem for me is the bright pink background. Work around it if it's a given that you cannot change, but do not be responsible for choosing it. Pink or red is particularly bad as a background, because chromatic aberration in an eye always forces it forwards from the plane of a neutral screen.