For each PDF/A-1 validation issue we try to explain what it means and, if possible how to resolve it. For a more technical explanation of the issue we quote the related section of the ISO 19005-1 PDF/A Specification.
All colours shall be specified in a device-independent manner, either directly by the use of a deviceindependent colour space, or indirectly by the use of an OutputIntent. A conforming file may use any colour space specified in PDF Reference, except as restricted in 6.2.3.2 to 6.2.3.4 of the ISO 19005-1:2205(E) Publication.
NOTE Specifying colour in the device-independent manner described within 6.2.3 of the ISO 19005-1:2205(E) Publication enables predictable colour rendering based on a colorimetric definition and without reliance on assumptions or information external to the conforming file. It also provides a mechanism whereby a colorimetric definition can be associated with device-dependent colour data.