Blue Bar vs Red Bar in disk utility

[inscrewtable]

Sometimes an SD card will show a blue bar in Disk Utility and other times it will show a red bar, what does the red bar mean?

 

[KALLT]

It is just a colour to help you distinguish the partitions. Red seems to be used for the second partition, whereas blue is used for the first. Sometimes you will have disk images that have a tiny first partition and a larger second partition, making the bar effectively completely red.