Slitherine

Various leaders have different shades of red. The land leader's stats (usually?) only involve better attack/defense vs soft/hard targets.
Do the various shades mean anything? Better stats equals bigger shade?

Not sure if I understand you right: to me it looks like different red tones are just the result of opacity and the terrain below shining through. How far the shaded red parts extent should indicate the leader's range (so whether he's affecting more units around him, or just his own unit, like in the 1st pic)

OK, so the leader affect all units within his shaded range. Good.

Besides the funny look, I can't tell you if all bonuses apply correctly on adjacent units, but I've tested a shock+assault bonus leader radius that definitely gives the same bonuses to another unit attacking the enemy. The additional shock and lesser entrenchment was there.
It would be nice if the bonus stats would not only show on the leader's unit stats but also on the affected allied units in the radius.

If the units are within the shaded are and their combat predictions are affected by the leader stat, that would work for me.