It does indicate blue bars

Negative US 2-10’s Yield Curve Doesn’t Indicate Recession

The flattening U.S. Treasury yield curve, traditionally believed to signal an oncoming recession, is no cause for alarm as the country’s economy continues to be strong, analysts say.The analysts who spoke to International Business Times also said the 2-10’s yield curve spread is not a reliable indicator of a recession. They note that it would be incorrect to use a single measure to draw conclusions on the prospects of the economy.

There we have it, when the line drops below zero a blue bar follows.