The dashed orange line is the preferred in room response "average" response based on whatever room(s) they used. The slope of the line will be different for every room and every listening distance, hence why the only target is the anechoic(left graph) flat(neutral) one. For example, I have speakers that are very anechoic neutral(
Genelec 8351b). They're essentially flat (within a couple db) from 30Hz to 18kHz, which is about as close to the Harman target as you can get. If I measure those speakers in my office(at ~1m), they measure almost flat. If I measure them in my living room at ~4m, they have an 8-10dB low to high slope. They sound neutral in both rooms, because they are neutral anechoically, and our brains have learned to "hear through the room".
This is completely different than with headphones, though, which is why I don't think it's a good comparison. Headphones don't have to deal with listening distance or room reflectivity. Honestly, if you're really just concerned with headphones, I would focus on that, and ignore the Harman speaker target. For headphones, the Etymotic curve is aimed towards a more neutral sounding response. The Harman headphone target is a bass boosted response. Harman headphone target and Harman loudspeaker target are very different in that regard.