That's because blue and orange are complementary colors - opposites on the color wheel. Imagine that I am dealing with a so-called white daylily. So we have yellow undertones to deal with. White would not be a good mate to this flower - it would merely make the ivory look dirty in contrast. But, if I prefer pastels I could use melon colors, which are really orange with a lot of white added.
Ivory is yellow with a lot of white.
And orange and yellow are neighbors on the color wheel . So would something in shades of green - the color on the other side of yellow on the wheel. Whether you go light or dark depends on whether you want drama or subtlety. You could also choose a flower in purple, which would be its opposite on the color wheel. My daylilies are not in bloom yet, so I can't show you that, but this photo of yellow hakonechloa contrasted with purple heuchera illustrates the principle of creating drama with contrasting colors.