i don’t know what i did but one of my bones has a different color now. it’s much brighter than the rest. no matter if selected or not. what does this mean? it doesn’t seem to affect anything but i would like to know. 
Any time a bone is moved in pose mode and applied with a keyframe it takes on a different color to let you know that is has been moved on that frame. There’s nothing wrong with it.
hm… no this doesn’t seem to be the reason. i can’t figure out what’s different with that bone.
what else could be the reason?
edit:
armature.blend (778 KB)
this is the blend file with my armature if you want to have a look.
The only way a bone can turn blue would be by inserting a keyframe after the bone is moved. After trying to clear it, my suggestion to you is to redo that part of the armature so you can eliminate the problem.
The bone is parented to the heel, change the parent to root like it’s opposite and the color will go away.
hm… the opposite wasn’t parented to root. both were parented to heel. but i changed the parent to root and then back to heel again and then color was gone. weird! i guess that was some kind of bug?
edit:
actually i was mixing up object mode with pose mode. 
the color is still there.
edit2:
deleting and recreating the bone was the only way of getting rid of it.