Today I found a bug in Apple's Mail program for Mac.
Select an email. Flag it with the yellow flag. Then give it an orange flag to change the flag color. Then click another email to unselect it.
The flag will display with a green color for about half a second. It fixes itself quickly.
I wonder if it's somehow using two colors at once and they mix to get green, or what. And I wonder why it fixes itself after that amount of time. Seems pretty strange. Software is hard!