I am creating PDF/X-1a output containing two colors: black and a spot color. The spot color is defined using @prince-color. The PDF has crop and cross marks enabled using @page marks. But when color separations are used for printing with different plates, then the marks only appear with the black output and not with the spot color output.

Is there any way to get crop and cross marks also output with the spot color?

We don't have that right now, but it might only require a modest extension, we will investigate.

In the Prince pre-release builds we have added a new prince-mark-color property, hope that helps!