Many substrates contain optical brighteners (also known as OBA's). These brighteners absorb ultraviolet (UV) light and reflect it into visible blue light, causing the human eye to see a more light than is actually shining on the brightened subject. A spectrophotometer will also detect this effect, but without a human brain to interpret the results, it has a tendency to read the white of your substrates as slightly more blue. Based on this information, your ICC profile calculations may result in a yellowish cast to 'fix' the blue.
If you aren't sure that the papers you are using have UV brightenters, a quick scan with a blacklight is the best way to check. And it's really fun.
So, now that you've determined that OBA's have made their way into your workflow what should you do to get the best results?
The answer depends on your hardware and software combination. Here's a handy review of X-Rite products and these filters:
ColorMunki - UV is always excluded.
i1Pro - Can be purchased with or without UV filter - check with your software manufacturer for recommended filter options, not interchangable.
i1iSis - UV excluded, UV included or dual measurements - check with your software manufacturer for recommended filter options
OBC (available with i1iSis) - After comparing the difference between UV included and UV excluded measurements a visual evaluation testchart is generated. Based on your visual feedback the software creates an ICC profile with the appropriate measurements for the amount of optical brighteners in your substrate.
i1Match - Optical brightener compensation will always be applied when UV brighteners are detected in your paper white measurement. Print with perceptual rendering intent for best results.
MonacoProfiler - UV filtered instruments are recommended.
ProfileMaker - Optical brightener compenstation will be available when UV brighteners are detected in your paper white measurement. Experiment by making profiles with the compensation on or off to see which setting is best for your substrate. Print with perceptual rendering intent for best results.