\colon gives correct spacing for a map
$F\colon C\to D$ in one direction. But writing
$L\colon C\rightleftarrows D\colon R$ for a couple of maps in both directions (e.g. for an adjunction) gives disturbingly asymmetric spaces near first and second colons (like if D were a map from R, not the other way round). Probably, it should be fixed (e.g. some other command should be used) — but how?