unit strength turning yellow or orange

[jjdenver]

What does it mean when the number on the unit representing its' strength (10, 9, 8, 7, etc) turns yellow then orange? And how do I turn it back to the normal white color? Thanks.

[Wavell1940]

This means that the efficiency of the unit has deteriorated. Efficiency includes unit cohesion, morale and fatigue. In order to get the unit number back to normal (white colour), remove it from combat and allow it to rest - no combat or movement. After a few turns it will recover.