there's some intra-Type variation between individuals, but in general, TCO and TDL feathers serve completely different purposes, which leads to different natural emotional postures.
aka function informs expression.
for example, TDL feathers don't have the strength to capture or repel physical attacks, so their only purpose is relaying heat outward. this function only works at a certain angle, so they are locked tight to the skin. if a conflict ends, they ruffle to unstick from the ready-state. a defensive individual might never flare its feathers voluntarily.
TCO armor is completely different, as i said. it functions best when it's tensed and ready to spring out, but the protection goes too far and that position blocks heat from getting to the skin. they have to loosen to stay warm. bristling in orderly rows is self-soothing, since this is the posture in which warmth is best allowed in, and it implies a long term stable situation.
TCOs are weak to fast attacks because the parry mechanism can be baited, then bypassed before it's ready to flare again.
TDLs in extreme stress may ripple repeatedly as they enter and exit a combat state.
blue jays' feathers are actually brown, and appear blue due to specific light scattering from oxygen in their feathers. before ignition, TCO feathers appear blue and shatter, fueling the resulting fireball. this is a separate process from iridescence, which is also distinct from cho's ice trick.
disturbing the layer of TDL feathers is super easy, like from water currents, exposing the loose particulate skin to radiation shaving-