Thank you for your post.
Our Development and Testing departments are already aware of this issue under Mac OS X 10.9.x (Mavericks). This issue does not occur under Mac OS X 10.8.x (Mountain Lion) nor Mac OS X 10.7.x (Lion).
I have attached your post to the original report. When any additional information becomes available, I will post again.
Until this is changed, continue using the RGB Slider to change the color.
An entry in the Known Bugs List has been linked to this Issue Report. Any Comments/Questions/Suggested Corrections should be posted here or in a new thread. Please do not post such comments to the Known Bugs List thread.
This issue has been addressed in FileMaker Pro 15.