you could try setting the unit's vertex color to blue with triggers:
trigger #1
event:
unit start the effect of an ability
cond:
ability = Bladestorm
action:
set BladeStormUnit=triggering unit
change triggering unit's vertex color to 0, 0, 100, 0
trigger #2
event:
unit finishes casting an ability (or ends channeling i dunno)
cond:
triggering unit = BladeStormUnit
action:
change triggering unit's vertex color to 100, 100, 100, 0
if it doesn't work, you must edit the model...