Not for the most part no. Ran, although a fantastic film, is similar in certain respects to a Hollywood version of a medieval film. There is historical accuracy but it was also made to look good.
Obviously clans and units in the clan would have the same sort of 'mon' (family crest) but it could change from unit to unit and if a lords retainers were sequestered by a higher lord for a big fight then sometimes sashimono would get supplied, but they wouldn't all be the same and of course if smaller units got merged into larger ones then armour would be mixed along with pretty much everything else.
There were no hard and fast rules to the implementation of heraldry in Sengoku Japan. The mon could be passed down through the family (and generally was) but it was up to the individual on how it was displayed, colours used, arrangement etc.
For gaming (depending on which figure ratio you go for) painting a unit with the same sashimono would certainly be OK, especially the smaller engagements. But for the big buggers like Sekigahara, units would be more suitable if there was a mix of mon, colour, armour colour etc.
Also for gaming, having 'armies' in a certain colour helps and makes the game look rather good
Rambling a bit but hopefully you get the idea
cheers
James