Ran across a bug today concerning blink and transparent BG controls.
I went back to 7.1 and saw one of the two issues.  The control background color is not set back to transparent on the "OFF" blink.  So, the blink BG color doesn't go away.  This bug also present in 8.0, 8.2, and 8.5.
The second bug started in 8.2.  The blink BG color is used instead of the blink FG color.  So, you will see the text in the control disappear on the "ON" blink.  This is still present in 8.5
This only appears to be an issue with controls with a transparent background as the attached test VI shows.