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I can see why the orange color for the input cells in IDF-Editor are giving you alarm. Normally, this indicates an input error. You are correct in stating that the EnergyPlus documentation makes it seem like these performance curves for chiller heater objects must be biquadratic or bilinear. The ultimate resource for proper input fields is ALWAYS the Energy+.idd file. If there is ever an inconsistency between the Input / Output Reference and the IDD file, the IDD file is always correct.

If you look at these performance curve input fields for the ChillerHeater:Absorption:DirectFired object in the IDD file, you'll notice that there are several options to choose from via an object-list:

• LinearCurves (collection of all Curve:Linear objects in the model)
• QuadraticCurves (collection of all Curve:Quadratic objects in the model)
• CubicCurves (collection of all Curve:Cubic objects in the model)
• QuarticCurves (collection of all Curve:Quartic objects in the model)
• ExponentCurves (collection of all Curve:Exponent objects in the model)
• UniVariateTables (collection of all Table:OneIndependentVariable and Table:MultiVariableLookup objects in the model)

For your case, trying to select a Biquadratic curve for this field doesn't match with what the IDD has as available options, so the cell is orange in IDF-Editor. This is why your quadratic curve is not orange, since quadratic curves are available options according to the IDD file.

If your file still runs and doesn't crash, then EnergyPlus SHOULD be using the performance curve correctly. To be sure, you can track the performance curve output value from the *.RDD file that gets generated after each EnergyPlus run. It should be

 HVAC,Average,Performance Curve Output Value []