Forever referrals will give you orange bars.

k00b

Hmm I updated the page and then I zoomed out and a small blue bar appeared showing one referrer for a few seconds and then it vanished, like if it was drained

felipe

SN release: new referral system part 2

Zoom out in the referral chart. 

If an existing stacker doesn't have a forever referrer, you refer them, then they login, you'll become their forever referrer. 

This referral is plotted when that stacker joined, which may have been years ago, not when the referral happened.