Does the use of various accessories affect the color balance?
It is quite possible for the brolly boxes and umbrellas (as well as other fabric-based accessories) to produce either warmer or colder color temperature, even from batch to batch. This is typical with most all fabric-based accessories
- the vendor buys the fabric and the fabric supplier gets it from different batches. It's pretty hard to control - even for the most expensive brands.
The same is true with basic flash color temperature and cameras. 5600° K might be neutral on one camera and 300-400° off on another camera. There is also a green/red component of color balance that is not stated in the basic color temperature specs, so even an exact match in color temperature alone will not yield perfectly neutral color balance.
There is a lot of controversy about this subject, and the consensus is that one cannot rely on color specs or camera settings to achieve perfect color balance - with any lights or accessories. The consensus also is that all accessories will alter color balance by up to several hundred degrees.
The only way to properly color balance is to do a custom white balance in the camera
or, preferably, to shoot in RAW and color balance in Photoshop or other RAW program
>> Click Here for more detailed info on Color Temperature / Color Balance - including instructions to help you achieve excellent color balance