In InDesign there is an option to specify the transarency blend color space. Is there something equivalent to this in Illustrator? If not, how does Illustrator set the colorspace (CMYK or RGB) for transparent elements? In printing we can get all kinds of problems with transparency problems such as boxes, if the transparency space differs from the image's working space. I want to find a way to sync this so the transparency blends all match the working space. Typically I work in CMYK. Thanks.
Ai offers you either RGB or CMYK; you decide which in the File > Document Color Mode ( circa v10 ). Transparency doesn't care which space you use in Ai. If you work in CMYK, then just make sure your swatches and images are CMYK. But, I think there are other reasons why you'd get boxes in transparent objects. Take a look at Flattening.