Now here is a tip I learned recently and I'm probably the last person to figure this out, but I thought I would share here just in case I wasn't.
When photographing cards that are quite 'white' I find that unless I use a very dark (preferably black) background the white on the cards can look quite pink in colour.
Here are a couple of examples.
All of these cards were taken with the same camera in the same room at the same time, no changes in settings (all on auto setting) and no post editing done other than cropping and adding the watermark.
Hope this helps someone else ... I can't believe it took me so long to figure it out myself!